Add support for folder-specific settings (#2537)

This PR allows you to customize Zed's settings within a particular
folder by creating a `.zed/settings.json` file within that folder.

Todo

* [x] respect folder-specific settings for local projects
* [x] respect folder-specific settings in remote projects
* [x] pass a path when retrieving editor/language settings
* [x] pass a path when retrieving copilot settings
* [ ] update the `Setting` trait to make it clear which types of
settings are locally overridable

Release Notes:

* Added support for folder-specific settings. You can customize Zed's
settings within a particular folder by creating a `.zed` directory and a
`.zed/settings.json` file within that folder.

crates/project/src/lsp_command.rs

@@ -1717,8 +1717,7 @@ impl LspCommand for OnTypeFormatting {
             .await?;
 
         let tab_size = buffer.read_with(&cx, |buffer, cx| {
-            let language_name = buffer.language().map(|language| language.name());
-            language_settings(language_name.as_deref(), cx).tab_size
+            language_settings(buffer.language(), buffer.file(), cx).tab_size
         });
 
         Ok(Self {