fix(developer): chiral mismatch warning is disruptive

Fixes #4803.

This fixes part of #4803 - namely the obtrusive warning flagging that
there are mismatched modifier types in the keyboard. Instead of making
the change during tab switching, it simply shows a warning message in
the design view of the keyboard, which the developer can choose to
ignore.

This does not address the removal of comments or the switch of character
formats which is part of that conversion routine. That is a more complex
change to the parser.