Add a setting for custom associations between languages and files (#9290)

Closes #5178

Release Notes:

- Added a `file_types` setting that can be used to associate languages
with file names and file extensions. For example, to interpret all `.c`
files as C++, and files called `MyLockFile` as TOML, add the following
to `settings.json`:

    ```json
    {
      "file_types": {
        "C++": ["c"],
        "TOML": ["MyLockFile"]
      }
    }
    ```

As with most zed settings, this can be configured on a per-directory
basis by including a local `.zed/settings.json` file in that directory.

---------

Co-authored-by: Marshall <marshall@zed.dev>

crates/settings/src/settings.rs

@@ -8,7 +8,7 @@ use util::asset_str;
 
 pub use keymap_file::KeymapFile;
 pub use settings_file::*;
-pub use settings_store::{Settings, SettingsJsonSchemaParams, SettingsStore};
+pub use settings_store::{Settings, SettingsJsonSchemaParams, SettingsLocation, SettingsStore};
 
 #[derive(RustEmbed)]
 #[folder = "../../assets"]