Add mouse navigation button support for actions

# Description of the new feature/enhancement
Follow-up on #10801: the added `browser_back` and `_forward` keys are the keyboard keys, not the mouse buttons. It might be nice to add support for these buttons as well, usually they are `VK_XBUTTON1` and `VK_XBUTTON2`.

# Proposed technical implementation details (optional)

The implementation will be a bit more complicated than just adding the key definitions, as now the mouse handlers should also check for keychord bindings. My proposal would be to add this to `TermControl::_PointerPressedHandler`. This would limit the support to when hovering the terminal control, so that might not be ideal. I am not sure what is actually desirable here.

Things to consider:
- Add support for "just" XBUTTON1/2, or also for other buttons?
- What should the textual representation of these buttons be? Make them coincide with `browser_back` and `_forward`, or separate names `mouse_back` and `_forward`?
- How do mouses with more macro buttons operate?

Start by reviewing the related issue #10801 and the proposed TermControl::_PointerPressedHandler entry point. Determine the desired scope for VK_XBUTTON1/VK_XBUTTON2, naming, keychord handling, and additional mouse buttons before identifying the relevant tests or acceptance criteria; the issue is done when the agreed mouse-button behavior is implemented and verified.

Written by the indexing model from the issue text.