[LVGL] - Add Buttonmatrix functions to Flow

[derWarst]

Is your feature request related to a problem? Please describe.
I'm designing an interface that heavily relies on button matrices interacting with each other and it would be great if I could build this with the eez flow..

Describe the solution you'd like
Add Buttonmatrix functions
[lv_buttonmatrix_set_button_ctrl], [lv_buttonmatrix_set_button_ctrl]
and
'[lv_buttonmatrix_set_map]
[lv_buttonmatrix_set_ctrl_map]
'

to the EEZ flow.