Move some classes from the main gui module. (#12105)
Code layout in the gui module is sup optimal. This can easily cause cyclic imports for one such example see #11950
While the issue mentioned above has been resolved it makes sense to reorganize this part of the code to minimize likelihood of similar problems in the future.
Description of how this pull request fixes the issue:
- `LauncherDialog`, `WelcomeDialog` and `AskAllowUsageStatsDialog` were moved to the `gui.startupDialogs` module
- `getDocFilePath` has been moved into the new `documentationUtils` module as there is no logical connection between it and gui
Co-authored-by: buddsean <sean@nvaccess.org>
