Use native file and message dialogs on Linux desktop

[gtritchie]

The long-standing issue of Electron showing the file and message dialogs behind the main window has been fixed and should appear in an upcoming Electron release.

electron/electron#32857

We worked around this bug on Linux by adding an option to use the web-based dialogs (same as RStudio Server) and turned it on by default only on Linux: #11184

Once we've confirmed the fix is in the version of Electron we're using, we should consider changing the default for Linux (and possibly discuss if we should ditch this option to use web-based dialogs on Desktop altogether to simplify the testing matrix).

[ronblum]

^ ignore that "mentioned this issue"--that was a typo, wrong issue.

[ronblum]

Note: The non-native dialogs are needed for automated testing.