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/client/src/client.rs

@@ -28,7 +28,7 @@ use release_channel::{AppVersion, ReleaseChannel};
 use rpc::proto::{AnyTypedEnvelope, EntityMessage, EnvelopedMessage, PeerId, RequestMessage};
 use schemars::JsonSchema;
 use serde::{Deserialize, Serialize};
-use settings::{Settings, SettingsStore};
+use settings::{Settings, SettingsSources, SettingsStore};
 use std::fmt;
 use std::{
     any::TypeId,
@@ -97,15 +97,11 @@ impl Settings for ClientSettings {
 
     type FileContent = ClientSettingsContent;
 
-    fn load(
-        default_value: &Self::FileContent,
-        user_values: &[&Self::FileContent],
-        _: &mut AppContext,
-    ) -> Result<Self>
+    fn load(sources: SettingsSources<Self::FileContent>, _: &mut AppContext) -> Result<Self>
     where
         Self: Sized,
     {
-        let mut result = Self::load_via_json_merge(default_value, user_values)?;
+        let mut result = sources.json_merge::<Self>()?;
         if let Some(server_url) = &*ZED_SERVER_URL {
             result.server_url = server_url.clone()
         }
@@ -427,21 +423,19 @@ impl settings::Settings for TelemetrySettings {
 
     type FileContent = TelemetrySettingsContent;
 
-    fn load(
-        default_value: &Self::FileContent,
-        user_values: &[&Self::FileContent],
-        _: &mut AppContext,
-    ) -> Result<Self> {
+    fn load(sources: SettingsSources<Self::FileContent>, _: &mut AppContext) -> Result<Self> {
         Ok(Self {
-            diagnostics: user_values.first().and_then(|v| v.diagnostics).unwrap_or(
-                default_value
+            diagnostics: sources.user.as_ref().and_then(|v| v.diagnostics).unwrap_or(
+                sources
+                    .default
                     .diagnostics
                     .ok_or_else(Self::missing_default)?,
             ),
-            metrics: user_values
-                .first()
+            metrics: sources
+                .user
+                .as_ref()
                 .and_then(|v| v.metrics)
-                .unwrap_or(default_value.metrics.ok_or_else(Self::missing_default)?),
+                .unwrap_or(sources.default.metrics.ok_or_else(Self::missing_default)?),
         })
     }
 }