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/language/src/language.rs

@@ -38,6 +38,7 @@ use schemars::{
 use serde::{de, Deserialize, Deserializer, Serialize, Serializer};
 use serde_json::Value;
 use smol::future::FutureExt as _;
+use std::num::NonZeroU32;
 use std::{
     any::Any,
     cell::RefCell,
@@ -73,6 +74,8 @@ pub use syntax_map::{OwnedSyntaxLayer, SyntaxLayer};
 pub use text::LineEnding;
 pub use tree_sitter::{Parser, Tree};
 
+use crate::language_settings::SoftWrap;
+
 /// Initializes the `language` crate.
 ///
 /// This should be called before making use of items from the create.
@@ -99,6 +102,7 @@ lazy_static! {
     pub static ref PLAIN_TEXT: Arc<Language> = Arc::new(Language::new(
         LanguageConfig {
             name: "Plain Text".into(),
+            soft_wrap: Some(SoftWrap::PreferredLineLength),
             ..Default::default()
         },
         None,
@@ -576,6 +580,17 @@ pub struct LanguageConfig {
     /// The names of any Prettier plugins that should be used for this language.
     #[serde(default)]
     pub prettier_plugins: Vec<Arc<str>>,
+
+    /// Whether to indent lines using tab characters, as opposed to multiple
+    /// spaces.
+    #[serde(default)]
+    pub hard_tabs: Option<bool>,
+    /// How many columns a tab should occupy.
+    #[serde(default)]
+    pub tab_size: Option<NonZeroU32>,
+    /// How to soft-wrap long lines of text.
+    #[serde(default)]
+    pub soft_wrap: Option<SoftWrap>,
 }
 
 #[derive(Clone, Debug, Serialize, Deserialize, Default, JsonSchema)]
@@ -660,6 +675,9 @@ impl Default for LanguageConfig {
             prettier_parser_name: None,
             prettier_plugins: Default::default(),
             collapsed_placeholder: Default::default(),
+            hard_tabs: Default::default(),
+            tab_size: Default::default(),
+            soft_wrap: Default::default(),
         }
     }
 }