Add hidden --extension to override inference of source type from file extension (#8373)

## Summary

This PR addresses the incompatibility with `jupyterlab-lsp` +
`python-lsp-ruff` arising from the inference of source type from file
extension, raised in #6847.

In particular it follows the suggestion in
https://github.com/astral-sh/ruff/issues/6847#issuecomment-1765724679 to
specify a mapping from file extension to source type.

The source types are

- python
- pyi
- ipynb

Usage:

```sh
ruff check --no-cache --stdin-filename Untitled.ipynb --extension ipynb:python
```

Unlike the original suggestion, `:` instead of `=` is used to associate
file extensions to language since that is what is used with
`--per-file-ignores` which is an existing option that accepts a mapping.

## Test Plan

2 tests added to `integration_test.rs` to ensure the override works as
expected

---------

Co-authored-by: Charlie Marsh <charlie.r.marsh@gmail.com>

crates/ruff_workspace/src/configuration.rs

@@ -25,8 +25,8 @@ use ruff_linter::rule_selector::{PreviewOptions, Specificity};
 use ruff_linter::rules::pycodestyle;
 use ruff_linter::settings::rule_table::RuleTable;
 use ruff_linter::settings::types::{
-    FilePattern, FilePatternSet, PerFileIgnore, PreviewMode, PythonVersion, SerializationFormat,
-    UnsafeFixes, Version,
+    ExtensionMapping, FilePattern, FilePatternSet, PerFileIgnore, PreviewMode, PythonVersion,
+    SerializationFormat, UnsafeFixes, Version,
 };
 use ruff_linter::settings::{
     resolve_per_file_ignores, LinterSettings, DEFAULT_SELECTORS, DUMMY_VARIABLE_RGX, TASK_TAGS,
@@ -216,6 +216,7 @@ impl Configuration {
             linter: LinterSettings {
                 rules: lint.as_rule_table(lint_preview),
                 exclude: FilePatternSet::try_from_iter(lint.exclude.unwrap_or_default())?,
+                extension: lint.extension.unwrap_or_default(),
                 preview: lint_preview,
                 target_version,
                 project_root: project_root.to_path_buf(),
@@ -523,6 +524,7 @@ impl Configuration {
 pub struct LintConfiguration {
     pub exclude: Option<Vec<FilePattern>>,
     pub preview: Option<PreviewMode>,
+    pub extension: Option<ExtensionMapping>,
 
     // Rule selection
     pub extend_per_file_ignores: Vec<PerFileIgnore>,
@@ -589,6 +591,9 @@ impl LintConfiguration {
             .chain(options.common.extend_unfixable.into_iter().flatten())
             .collect();
         Ok(LintConfiguration {
+            // `--extension` is a hidden command-line argument that isn't supported in configuration
+            // files at present.
+            extension: None,
             exclude: options.exclude.map(|paths| {
                 paths
                     .into_iter()
@@ -905,6 +910,7 @@ impl LintConfiguration {
         Self {
             exclude: self.exclude.or(config.exclude),
             preview: self.preview.or(config.preview),
+            extension: self.extension.or(config.extension),
             rule_selections: config
                 .rule_selections
                 .into_iter()