Added test_beginning_of_line_stop_at_indent editor test

- Follow-up to: https://github.com/zed-industries/zed/pull/25428
- Replaces: https://github.com/zed-industries/zed/pull/25346

This is all authored by @felixpackard in #25346
I just updated it to use `stop_at_indent` instead of
`stop_at_first_char`.

Release Notes:

- Added support for `stop_at_indent` to
`Editor::DeleteToBeginningOfLine` (thanks
[@felixpackard](https://github.com/felixpackard))

Co-authored-by: Felix Packard <felix@rigr.gg>