Linux Keybinding Improvements (#14600)

- Fixed ctrl-shift-d (duplicate line) conflict.
- Fixes #14458
- Remove some duplicated definitions
- Fix Expand/Shrink selection (was ctrl-shift-up/down, now alt-shift-left/right)
- Add `ctrl-f2` / `cmd-f2` as alias for `editor::SelectAllMatches` matching VSCode
- Moved multi-cursor (Insert cursor above / below) from ctrl-shift-up/down to alt-shift-up/down