Revert "Create a `MessageDialog` API (#17304)" (#17561)
This reverts commit 2477780dd3e9b1f44b73fee2a180a4f20553bdf4.
Reverts #17304
Issues fixed
Fixes #17560
Fixes #17553
Issues reopened
Reopens #13007
Reopens #12344
Reopens #12353
Reason for revert
This PR broke two important NVDA functions, and there is insufficient time before the Christmas/New Years break to fix the issues, so we are temporarily reverting so that alphas work over the break:
• The CRFT no longer works, as gui.message.MessageDialog's inheritance from ContextHelpMixin was accidentally removed.
• Update checking no longer works, as runScriptModalDialog was modified to increment and decrement _messageBoxCounter, but UpdateAskInstallDialog attempts to restart NVDA before it has been closed, so the update fails as NVDA appears to be in an unsafe state.
