feat(developer): New Project opens in new process

Fixes #10138.

If the current instance of Keyman Developer already has a project open,
then the New Project dialog will now open the new project in a new
instance of Keyman Developer.

Note: this also moves a couple of functions out of dmActionsMain and
into UfrmMain, as their functionality belongs more closely there. The
`TmodActionsMain.OpenProject` function has been renamed to
`TfrmMain.OpenProjectInCurrentProcess` to clarify its usage and context.