Support cell-by-cell navigation to allow links to be keyboard accessible and more fine grained keyboard selection

[Tyriar]

Two potential solutions:

• Allow navigating the buffer cell by cell and maybe enter to activate a link
• Enter a "link navigation mode" which allows navigating through just links (this is handled by the open/detect link commands
• Shift to select text

[Tyriar]

The discussion in xtermjs/xterm.js#583 (comment) affects how this would be implemented so it's blocked on that.

[Tyriar]

#87579 asks for selecting up page/cell, updated the title.