All displays currently used with ZMK are monochrome so it makes sense
to enable the mono theme by default, which can be disabled by the user
since we use the "imply" statement.
Without this theme setting, the small font size selection for widgets
at the bottom of the stock status screen does not work.
* LV_ prefix from new LVGL official Kconfig now used.
* API changes for themes, container object removal, etc.
* Add our own Kconfig and code for theme default small font.
* Remove some hardcoded sizes.
* Add new Kconfig settingsx to allow selecting system or dedicated
work queue for performing UI updates.
* Allow UI updates to not block other system tasks when display is
updating, especially important for e-ink displays.
