Allow user to use multiple formatters (#14846)

Fixes #4822
- [x] Release note
- [ ] Surface formatting errors via a toast
- [x] Doc updates
- [x] Have "language-server" accept an optional name of the server.

Release Notes:

- `format` and `format_on_save` now accept an array of formatting
actions to run.
- `language_server` formatter option now accepts the name of a language
server to use (e.g. `{"language_server": {"name: "ruff"}}`); when not
specified, a primary language server is used.

---------

Co-authored-by: Thorsten <thorsten@zed.dev>

docs/src/configuring-zed.md

@@ -601,6 +601,21 @@ To override settings for a language, add an entry for that language server's nam
 }
 ```
 
+4. Or to use multiple formatters consecutively, use an array of formatters:
+```json
+{
+  "formatter": [
+    {"language_server": {"name": "rust-analyzer"}},
+    {"external": {
+      "command": "sed",
+      "arguments": ["-e", "s/ *$//"]
+    }
+  ]
+}
+```
+Here `rust-analyzer` will be used first to format the code, followed by a call of sed.
+If any of the formatters fails, the subsequent ones will still be executed.
+
 ## Code Actions On Format
 
 - Description: The code actions to perform with the primary language server when formatting the buffer.