[LVGL] Add lv_indev_set_group action for encoder / keypads

[zalexzperez]

Is your feature request related to a problem? Please describe.
When we want to unfocus a widget to avoid accidental presses, one workaround is to set the focus to a dummy widget.

Describe the solution you'd like
Implement an lv_indev_set_group(enc_indev, enc_group) action.
Passing null as the second argument unsets the destination group for the input device, solving the problem.

Additional information
mvladic's words: the tricky part is to be able to provide the first argument. His idea:
We can have Get Group Indev with props "Group" and "Encoder type". This will return lv_indev_t * for the given group and encoder type and use returned value in the Set Indev Group action.