Automatically indent the cursor when adding a newline after a `{` in Gleam code files (#8097)

Fixes: https://github.com/zed-industries/zed/issues/7295

Release Notes:

- Fixed a bug where adding a newline after a `{` would not automatically
indent the cursor in Gleam code files
([#7295](https://github.com/zed-industries/zed/issues/7295)).