Added a new unassigned gesture to toggle keyboard layout (#19349)
Closes #19211
### Summary of the issue:
There was no command to toggle keyboard layout (desktop / laptop). It
may be useful for testing, or for someone switching between built-in and
external keyboard.
### Description of user facing changes:
* Added an unassigned command to toggle keyboard layout.
### Description of developer facing changes:
N/A
### Description of development approach:
Added the command script in `globalCommands.py`.
### Testing strategy:
Manual test
### Known issues with pull request:
None
