Keyboard: Create a setting for the style of the cursor in keyboard mode

[C-Loftus]

Currently there is no way to customize the type/style of cursor that Cursorless uses in keyboard mode. Having a separate cursor type would help to add extra contrast if needed. For accessibility reasons, the standard cursor style that the user prefers (i.e. line or outline block) may not provide enough contrast for some users (particularly cursorless has highlighted text). Thus, they may want to use a filled in block cursor to add more contrast.

According to discussion with Pokey, there does not seem to be a way to change cursor color. And with regards to styling this is probably unnecessary and should be controlled by the user's theme.