Add support for saving and opening files (#325)

* Add support for saving a document

This is similar to the "export" functionality, except that
we store all metadata needed to open the file again.

Currently we store the internal representation of the layer
which is probably pretty fragile.

Example document:

```json
{
    "nodes": {},
    "root": {
        "blend_mode": "Normal",
        "cache": "...",
        "cache_dirty": false,
        "data": {
            "Folder": {
                "layer_ids": [
                    3902938778642561358
                ],
                "layers": [
                    {
                        "blend_mode": "Normal",
                        "cache": "...",
                        "cache_dirty": false,
                        "data": {
                            "Shape": {
                                "path": [
                                    {
                                        "MoveTo": {
                                            "x": 0.0,
                                            "y": 0.0
                                        }
                                    },
                                    {
                                        "LineTo": {
                                            "x": 1.0,
                                            "y": 0.0
                                        }
                                    },
                                    {
                                        "LineTo": {
                                            "x": 1.0,
                                            "y": 1.0
                                        }
                                    },
                                    {
                                        "LineTo": {
                                            "x": 0.0,
                                            "y": 1.0
                                        }
                                    },
                                    "ClosePath"
                                ],
                                "render_index": 1,
                                "solid": true,
                                "style": {
                                    "fill": {
                                        "color": {
                                            "alpha": 1.0,
                                            "blue": 0.0,
                                            "green": 0.0,
                                            "red": 0.0
                                        }
                                    },
                                    "stroke": null
                                }
                            }
                        },
                        "name": null,
                        "opacity": 1.0,
                        "thumbnail_cache": "...",
                        "transform": {
                            "matrix2": [
                                223.0,
                                0.0,
                                -0.0,
                                348.0
                            ],
                            "translation": [
                                -188.0,
                                -334.0
                            ]
                        },
                        "visible": true
                    }
                ],
                "next_assignment_id": 3902938778642561359
            }
        },
        "name": null,
        "opacity": 1.0,
        "thumbnail_cache": "...",
        "transform": {
            "matrix2": [
                1.0,
                0.0,
                0.0,
                1.0
            ],
            "translation": [
                479.0,
                563.0
            ]
        },
        "visible": true
    },
    "version": 0
}
```

* Add support for opening a saved document

User can select a file using the browser's file input selector.
We parse it as JSON and load it into the internal representation.

Concerns:
- The file format is fragile
- Loading data directly into internal data structures usually creates
security vulnerabilities
- Error handling: The user is not informed of errors

* Serialize Document and skip "cache" fields in Layer

Instead of serializing the root layer, we serialize the
Document struct directly. Additionally, we mark the
"cache" fields in layer as "skip" fields so they
don't get serialized.

* Opened files use the filename as the tab title

* Split "new document" and "open document" handling

Open document needs name and content to be provided so having a
different interface is cleaner. Also did some refactoring to reuse code.

* Show error to user when a file fails to open

* Clean up code: better variable naming and structure

* Use document name for saved and exported files

We pass through the document name in the export and save
messages. Additionally, we check if the appropriate file
suffixes (.graphite and .svg) need to be added before
passing it to the frontend.

* Refactor document name generation

* Don't assign a default of 1 to Documents that start with something
  other than DEFAULT_DOCUMENT_NAME
* Improve runtime complexity by using binary instead of linear search

* Update Layer panel upon document selection

* Add File>Open/Ctrl+O; File>Save (As)/Ctrl+(Shift)+S; browse filters extension; split out download()/upload() into files.ts; change unsaved close dialog text

Co-authored-by: Dennis Kobert <dennis@kobert.dev>
Co-authored-by: Keavon Chambers <keavon@keavon.com>

frontend/wasm/src/document.rs

@@ -69,6 +69,21 @@ pub fn new_document() -> Result<(), JsValue> {
 	EDITOR_STATE.with(|editor| editor.borrow_mut().handle_message(DocumentsMessage::NewDocument).map_err(convert_error))
 }
 
+#[wasm_bindgen]
+pub fn open_document() -> Result<(), JsValue> {
+	EDITOR_STATE.with(|editor| editor.borrow_mut().handle_message(DocumentsMessage::OpenDocument).map_err(convert_error))
+}
+
+#[wasm_bindgen]
+pub fn open_document_file(name: String, content: String) -> Result<(), JsValue> {
+	EDITOR_STATE.with(|editor| editor.borrow_mut().handle_message(DocumentsMessage::OpenDocumentFile(name, content)).map_err(convert_error))
+}
+
+#[wasm_bindgen]
+pub fn save_document() -> Result<(), JsValue> {
+	EDITOR_STATE.with(|editor| editor.borrow_mut().handle_message(DocumentMessage::SaveDocument)).map_err(convert_error)
+}
+
 #[wasm_bindgen]
 pub fn close_document(document: usize) -> Result<(), JsValue> {
 	EDITOR_STATE.with(|editor| editor.borrow_mut().handle_message(DocumentsMessage::CloseDocument(document)).map_err(convert_error))

frontend/wasm/src/wrappers.rs

@@ -1,9 +1,25 @@
 use crate::shims::Error;
+use editor::consts::FILE_SAVE_SUFFIX;
 use editor::input::keyboard::Key;
 use editor::tool::{SelectAppendMode, ToolType};
 use editor::Color as InnerColor;
 use wasm_bindgen::prelude::*;
 
+#[wasm_bindgen]
+pub fn file_save_suffix() -> String {
+	FILE_SAVE_SUFFIX.into()
+}
+
+#[wasm_bindgen]
+pub fn i32_max() -> i32 {
+	i32::MAX
+}
+
+#[wasm_bindgen]
+pub fn i32_min() -> i32 {
+	i32::MIN
+}
+
 #[wasm_bindgen]
 pub struct Color(InnerColor);