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/terminal/src/terminal_settings.rs

@@ -7,7 +7,7 @@ use schemars::{
 };
 use serde_derive::{Deserialize, Serialize};
 use serde_json::Value;
-use settings::SettingsJsonSchemaParams;
+use settings::{SettingsJsonSchemaParams, SettingsSources};
 use std::path::PathBuf;
 
 #[derive(Copy, Clone, Debug, Serialize, Deserialize, JsonSchema, PartialEq, Eq)]
@@ -171,12 +171,12 @@ impl settings::Settings for TerminalSettings {
     type FileContent = TerminalSettingsContent;
 
     fn load(
-        default_value: &Self::FileContent,
-        user_values: &[&Self::FileContent],
+        sources: SettingsSources<Self::FileContent>,
         _: &mut AppContext,
     ) -> anyhow::Result<Self> {
-        Self::load_via_json_merge(default_value, user_values)
+        sources.json_merge()
     }
+
     fn json_schema(
         generator: &mut SchemaGenerator,
         params: &SettingsJsonSchemaParams,