Release 2.15.0

Removals

MirAL bumped to 4.0, removed previously deprecated:

• mir_keyboard_event_key_code
• WaylandExtensions::set_filter
• WaylandExtensions::zwp_virtual_keyboard_v1
• WaylandExtensions::zwp_virtual_input_v1
• WindowManagementPolicy::handle_request_drag_and_drop
• WindowManagerTools::start_drag_and_drop
• WindowManagerTools::end_drag_and_drop

ABI summary:

• miral ABI bumped to 6
• mirserver ABI bumped to 59
• mirwayland ABI bumped to 4

Packaging changes:

• [debian] mir-doc dropped in favour of online documentation

Enhancements:

• [doc] publish API documentation on ReadTheDocs
  https://canonical-mir.readthedocs-hosted.com/
• [window management] improved Alt+Tab behaviour #2981

Bugs fixed

• [input] keyboard meta key state gets out of step #2985