Implements the following keyboard selection non-configurable key bindings:
- shift+arrow --> move endpoint by character
- ctrl+shift+left/right --> move endpoint by word
- shift+home/end --> move to beginning/end of line
- ctrl+shift+home/end --> move to beginning/end of buffer
This was purposefully done in the ControlCore layer to make keyboard selection an innate part of how the terminal functions (aka a shared component across terminal consumers).
## References
#715 - Keyboard Selection
#2840 - Spec
## Detailed Description of the Pull Request / Additional comment
The most relevant section is `TerminalSelection.cpp`, where we define how each movement operates. It's basically a giant embedded switch-case statement. We leverage a lot of the work done in a11y to perform the movements.
## Validation Steps Performed
- General cases:
- test all of the key bindings added
- Corner cases:
- `char`: wide glyph support
- `word`: move towards, away, and across the selection pivot
- automatically scroll viewport
- ESC (and other key combos) are still clearing the selection properly
c070be12d3