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/tasks_ui/src/settings.rs

@@ -1,5 +1,6 @@
 use schemars::JsonSchema;
 use serde::{Deserialize, Serialize};
+use settings::{Settings, SettingsSources};
 
 #[derive(Serialize, Deserialize, PartialEq, Default)]
 pub(crate) struct TaskSettings {
@@ -13,22 +14,15 @@ pub(crate) struct TaskSettingsContent {
     show_status_indicator: Option<bool>,
 }
 
-impl settings::Settings for TaskSettings {
+impl Settings for TaskSettings {
     const KEY: Option<&'static str> = Some("task");
 
     type FileContent = TaskSettingsContent;
 
     fn load(
-        default_value: &Self::FileContent,
-        user_values: &[&Self::FileContent],
+        sources: SettingsSources<Self::FileContent>,
         _: &mut gpui::AppContext,
-    ) -> gpui::Result<Self>
-    where
-        Self: Sized,
-    {
-        let this = Self::json_merge(default_value, user_values)?;
-        Ok(Self {
-            show_status_indicator: this.show_status_indicator.unwrap_or(true),
-        })
+    ) -> gpui::Result<Self> {
+        sources.json_merge()
     }
 }