reorg: move JS ops implementations to cli/js/ops/, part 3 (#4302)

Following JS ops were moved to separate files in cli/js/ops directory:
- net
- tls
- fs

cli/js/ops/fs/open.ts

@@ -0,0 +1,67 @@
+// Copyright 2018-2020 the Deno authors. All rights reserved. MIT license.
+import { sendSync, sendAsync } from "../dispatch_json.ts";
+
+export interface OpenOptions {
+  /** Sets the option for read access. This option, when `true`, means that the
+   * file should be read-able if opened. */
+  read?: boolean;
+  /** Sets the option for write access. This option, when `true`, means that
+   * the file should be write-able if opened. If the file already exists,
+   * any write calls on it will overwrite its contents, by default without
+   * truncating it. */
+  write?: boolean;
+  /**Sets the option for the append mode. This option, when `true`, means that
+   * writes will append to a file instead of overwriting previous contents.
+   * Note that setting `{ write: true, append: true }` has the same effect as
+   * setting only `{ append: true }`. */
+  append?: boolean;
+  /** Sets the option for truncating a previous file. If a file is
+   * successfully opened with this option set it will truncate the file to `0`
+   * length if it already exists. The file must be opened with write access
+   * for truncate to work. */
+  truncate?: boolean;
+  /** Sets the option to allow creating a new file, if one doesn't already
+   * exist at the specified path. Requires write or append access to be
+   * used. */
+  create?: boolean;
+  /** Defaults to `false`. If set to `true`, no file, directory, or symlink is
+   * allowed to exist at the target location. Requires write or append
+   * access to be used. When createNew is set to `true`, create and truncate
+   * are ignored. */
+  createNew?: boolean;
+}
+
+/** A set of string literals which specify the open mode of a file.
+ *
+ * |Value |Description                                                                                       |
+ * |------|--------------------------------------------------------------------------------------------------|
+ * |`"r"` |Read-only. Default. Starts at beginning of file.                                                  |
+ * |`"r+"`|Read-write. Start at beginning of file.                                                           |
+ * |`"w"` |Write-only. Opens and truncates existing file or creates new one for writing only.                |
+ * |`"w+"`|Read-write. Opens and truncates existing file or creates new one for writing and reading.         |
+ * |`"a"` |Write-only. Opens existing file or creates new one. Each write appends content to the end of file.|
+ * |`"a+"`|Read-write. Behaves like `"a"` and allows to read from file.                                      |
+ * |`"x"` |Write-only. Exclusive create - creates new file only if one doesn't exist already.                |
+ * |`"x+"`|Read-write. Behaves like `x` and allows reading from file.                                        |
+ */
+export type OpenMode = "r" | "r+" | "w" | "w+" | "a" | "a+" | "x" | "x+";
+
+export function openSync(
+  path: string,
+  mode: OpenMode | undefined,
+  options: OpenOptions | undefined
+): number {
+  return sendSync("op_open", { path, options, mode });
+}
+
+export async function open(
+  path: string,
+  mode: OpenMode | undefined,
+  options: OpenOptions | undefined
+): Promise<number> {
+  return await sendAsync("op_open", {
+    path,
+    options,
+    mode
+  });
+}