Add the ability for extensions to provide language settings (#10296)

This PR adds the ability for extensions to provide certain language
settings via the language `config.toml`.

These settings are then merged in with the rest of the settings when the
language is loaded from the extension.

The language settings that are available are:

- `tab_size`
- `hard_tabs`
- `soft_wrap`

Additionally, for bundled languages we moved these settings out of the
`settings/default.json` and into their respective `config.toml`s .

For languages currently provided by extensions, we are leaving the
values in the `settings/default.json` temporarily until all released
versions of Zed are able to load these settings from the extension.

---

Along the way we ended up refactoring the `Settings::load` method
slightly, introducing a new `SettingsSources` struct to better convey
where the settings are being loaded from.

This makes it easier to load settings from specific locations/sets of
locations in an explicit way.

Release Notes:

- N/A

---------

Co-authored-by: Max <max@zed.dev>
Co-authored-by: Max Brunsfeld <maxbrunsfeld@gmail.com>

crates/zed/src/zed.rs

@@ -607,6 +607,7 @@ pub fn handle_keymap_file_changes(
     cx.observe_global::<SettingsStore>(move |cx| {
         let new_base_keymap = *BaseKeymap::get_global(cx);
         let new_vim_enabled = VimModeSetting::get_global(cx).0;
+
         if new_base_keymap != old_base_keymap || new_vim_enabled != old_vim_enabled {
             old_base_keymap = new_base_keymap;
             old_vim_enabled = new_vim_enabled;
@@ -3062,6 +3063,7 @@ mod tests {
             let mut app_state = AppState::test(cx);
 
             let state = Arc::get_mut(&mut app_state).unwrap();
+            env_logger::try_init().ok();
 
             state.build_window_options = build_window_options;
             theme::init(theme::LoadThemes::JustBase, cx);