Keyboard cursor customization

[C-Loftus]

Addresses https://github.com/cursorless-dev/cursorless/issues/2401, the ability to have custom cursor styling exclusively when in cursorless keyboard mode.

Tried to follow the repo style as best as possible but please let me know if another way besides a record mapper is more idiomatic for TS.

Checklist

• [/] I have added tests
• [x] I have updated the docs and cheatsheet
  • I could add docs in the visual a11y section but unclear if experimental keyboard support belongs there
• [x] I have not broken the cheatsheet

Example

An image showing the cursor start out with a custom type, then change into block when keyboard mode is activated, thus adding more contrast.