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/language/src/language_registry.rs

@@ -1,3 +1,4 @@
+use crate::language_settings::{AllLanguageSettingsContent, LanguageSettingsContent};
 use crate::{
     language_settings::all_language_settings, task_context::ContextProvider, CachedLspAdapter,
     File, Language, LanguageConfig, LanguageId, LanguageMatcher, LanguageServerName, LspAdapter,
@@ -38,6 +39,7 @@ pub struct LanguageRegistry {
 struct LanguageRegistryState {
     next_language_server_id: usize,
     languages: Vec<Arc<Language>>,
+    language_settings: AllLanguageSettingsContent,
     available_languages: Vec<AvailableLanguage>,
     grammars: HashMap<Arc<str>, AvailableGrammar>,
     lsp_adapters: HashMap<Arc<str>, Vec<Arc<CachedLspAdapter>>>,
@@ -145,6 +147,7 @@ impl LanguageRegistry {
                 languages: Vec::new(),
                 available_languages: Vec::new(),
                 grammars: Default::default(),
+                language_settings: Default::default(),
                 loading_languages: Default::default(),
                 lsp_adapters: Default::default(),
                 subscription: watch::channel(),
@@ -338,6 +341,10 @@ impl LanguageRegistry {
         *state.subscription.0.borrow_mut() = ();
     }
 
+    pub fn language_settings(&self) -> AllLanguageSettingsContent {
+        self.state.read().language_settings.clone()
+    }
+
     pub fn language_names(&self) -> Vec<String> {
         let state = self.state.read();
         let mut result = state
@@ -854,6 +861,16 @@ impl LanguageRegistryState {
         if let Some(theme) = self.theme.as_ref() {
             language.set_theme(theme.syntax());
         }
+        self.language_settings.languages.insert(
+            language.name(),
+            LanguageSettingsContent {
+                tab_size: language.config.tab_size,
+                hard_tabs: language.config.hard_tabs,
+                soft_wrap: language.config.soft_wrap,
+                ..Default::default()
+            }
+            .clone(),
+        );
         self.languages.push(language);
         self.version += 1;
         *self.subscription.0.borrow_mut() = ();