Add a split keyboard toggle to the toolbar

[slashdevslashurandom]

Currently the split keyboard option can only be changed using the HeliBoard Settings panel. Whereas other features, such as singlehanded mode, autocorrect and incognito mode, can have toggle buttons added to the keyboard's toolbar, split keyboard cannot.

Describe the solution you'd like
A split keyboard toggle should be made available as a potential toolbar button and/or when holding the comma key.

Use case
A tablet user who frequently changes between landscape and portrait mode might want to turn split keyboard on and off frequently.

Describe alternatives you've considered (if any)
Alternatively, the split keyboard option could be separated into one for landscape mode and one for portrait mode, solving the specific use case mentioned.