Bug 1097450 - Save (to settings) the activeLayout of groups supported by one layout, when we change to that layout

- The whole currentActiveLayout logics have been consolidated from KeyboardHelper to InputLayouts, as part of our goal to disentangle KeyboardHelper.
- Also, properly define the undefiness of activeLayout in InputLayout's layouts.
Merge pull request #26104 from mnjul/bug_1097450_save_group_active_layout

Bug 1097450 - Save (to settings) the activeLayout of groups supported by one layout, when we change to that layout. r=timdream, f=johnhu