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/vim/src/vim.rs

@@ -35,7 +35,7 @@ use replace::multi_replace;
 use schemars::JsonSchema;
 use serde::Deserialize;
 use serde_derive::Serialize;
-use settings::{update_settings_file, Settings, SettingsStore};
+use settings::{update_settings_file, Settings, SettingsSources, SettingsStore};
 use state::{EditorState, Mode, Operator, RecordedSelection, WorkspaceState};
 use std::{ops::Range, sync::Arc};
 use surrounds::{add_surrounds, change_surrounds, delete_surrounds};
@@ -779,13 +779,9 @@ impl Settings for VimModeSetting {
 
     type FileContent = Option<bool>;
 
-    fn load(
-        default_value: &Self::FileContent,
-        user_values: &[&Self::FileContent],
-        _: &mut AppContext,
-    ) -> Result<Self> {
-        Ok(Self(user_values.iter().rev().find_map(|v| **v).unwrap_or(
-            default_value.ok_or_else(Self::missing_default)?,
+    fn load(sources: SettingsSources<Self::FileContent>, _: &mut AppContext) -> Result<Self> {
+        Ok(Self(sources.user.copied().flatten().unwrap_or(
+            sources.default.ok_or_else(Self::missing_default)?,
         )))
     }
 }
@@ -824,11 +820,7 @@ impl Settings for VimSettings {
 
     type FileContent = VimSettingsContent;
 
-    fn load(
-        default_value: &Self::FileContent,
-        user_values: &[&Self::FileContent],
-        _: &mut AppContext,
-    ) -> Result<Self> {
-        Self::load_via_json_merge(default_value, user_values)
+    fn load(sources: SettingsSources<Self::FileContent>, _: &mut AppContext) -> Result<Self> {
+        sources.json_merge()
     }
 }