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/journal/src/journal.rs

@@ -5,7 +5,7 @@ use editor::Editor;
 use gpui::{actions, AppContext, ViewContext, WindowContext};
 use schemars::JsonSchema;
 use serde::{Deserialize, Serialize};
-use settings::Settings;
+use settings::{Settings, SettingsSources};
 use std::{
     fs::OpenOptions,
     path::{Path, PathBuf},
@@ -50,12 +50,8 @@ impl settings::Settings for JournalSettings {
 
     type FileContent = Self;
 
-    fn load(
-        defaults: &Self::FileContent,
-        user_values: &[&Self::FileContent],
-        _: &mut AppContext,
-    ) -> Result<Self> {
-        Self::load_via_json_merge(defaults, user_values)
+    fn load(sources: SettingsSources<Self::FileContent>, _: &mut AppContext) -> Result<Self> {
+        sources.json_merge()
     }
 }