* 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.
The default configuration for corneish-zen enables a USB CDC endpoint by
default. This is most probably a debugging left-over. Disable that
endpoint. CONFIG_ZMK_USB_LOGGING depends on it anyway, so it will be
enabled again with that config option set.