Add code_actions as formatter type (#10121)

This fixes #8992 and solves a problem that ESLint/Prettier/... users
have been running into:

They want to format _only_ with ESLint, which is *not* a primary
language server (so `formatter: language server` does not help) and it
is not a formatter.

What they want to use is what they get when they have configured
something like this:

```json
{
  "languages": {
    "JavaScript": {
      "code_actions_on_format": {
        "source.fixAll.eslint": true
      }
    }
  }
}
```

BUT they don't want to run the formatter.

So what this PR does is to add a new formatter type: `code_actions`.

With that, users can only use code actions to format:

```json
{
  "languages": {
    "JavaScript": {
      "formatter": {
        "code_actions": {
          "source.fixAll.eslint": true
        }
      }
    }
  }
}
```

This means that when formatting (via `editor: format` or on-save) only
the code actions that are specified are being executed, no formatter.


Release Notes:

- Added a new `formatter`/`format_on_save` option: `code_actions`. When
configured, this uses language server code actions to format a buffer.
This can be used if one wants to, for example, format a buffer with
ESLint and *not* run prettier or another formatter afterwards. Example
configuration: `{"languages": {"JavaScript": {"formatter":
{"code_actions": {"source.fixAll.eslint": true}}}}}`
([#8992](https://github.com/zed-industries/zed/issues/8992)).

---------

Co-authored-by: JH Chabran <jh@chabran.fr>
Co-authored-by: Marshall Bowers <elliott.codes@gmail.com>

crates/project/src/prettier_support.rs

@@ -31,7 +31,9 @@ pub fn prettier_plugins_for_language<'a>(
 ) -> Option<&'a Vec<Arc<str>>> {
     match &language_settings.formatter {
         Formatter::Prettier { .. } | Formatter::Auto => {}
-        Formatter::LanguageServer | Formatter::External { .. } => return None,
+        Formatter::LanguageServer | Formatter::External { .. } | Formatter::CodeActions(_) => {
+            return None
+        }
     };
     if language.prettier_parser_name().is_some() {
         Some(language.prettier_plugins())