## Summary
- add an editor action for selecting the contents of the innermost
enclosing bracket pair
- register the action without assigning a default key binding
- cover cursor, selection, nested bracket, no-op, and multi-cursor cases

## Tests
- cargo fmt --check
- cargo test -p editor test_select_inside_enclosing_bracket --lib
- cargo test -p editor test_move_to_enclosing_bracket --lib

Release Notes:

- Added action to select the contents enclosed by brackets