This re-implements keyboard text selection so that it will work on platforms other than Android (e.g. macOS, Linux, etc.).

Also, fixed a number of bugs in editing selection via a hardware keyboard (unable to select backwards, incorrect conversion to ASCII when cutting to clipboard, lack of support for CTRL-SHIFT-ARROW word selection, etc.).

Did not address the keyboard locale issues that remain, or add platform specific switches for the bindings. All that will need some more design work before implementing them.

Related Issues
Fixes #31951