Making use of the new FileSystemAccessServer we are able to use
unveil without restricting our ability to open and save files.
A file argument will be unveiled automatically however all other files
require user action via the FileSystemAccessServer to gain access.
The HTML and Markdown preview modes both use an OutOfProcessWebView to
render the preview pane, and we were instantiating this view from GML.
This caused us to always spawn a WebContent process alongside every
TextEditor instance.
Fix this by deferring the OOPWV construction until we actually need it.
This makes launching TextEditor on a text file quite a bit faster. :^)
Instead of tracking this stuff ourselves at the application level,
we now just act as an intermediary and pass along the information to
the windowing system.
