Use GtkFileChooserNative to take advantage of the Flatpak file selection portal

[aperezdc]

Instead of letting WebKitGTK+ use GtkFileChooserDialog, Revolt should connect to WebKitWebView::run-file-chooser and use GtkFileChooserNative. The main motivation for this is enabling usage of the file chooser portal when running inside the Flatpak sandbox.

[aperezdc]

I am trying to get WebKitGTK+ to use GtkFileChooserNative directly. If the patches are accepted upstream, there would be nothing to do in Revolt. Unless we want to provide a fall-back for using with older WebKitGTK+ versions.

[aperezdc]

My patch was accepted upstream, but it would still be nice to provide a fallback for people using older releases of WebKitGTK+, we can use something like:

WEBKIT_VERSION = (WebKit2.get_major.version(),
                  WebKit2.get_minor_version(),
                  WebKit2.get_micro_version())

if WEBKIT_VERSION <= (2, 14, 5):
    # Connect to WebKitWebView::run-file-chooser

[aperezdc]

Using GNOME 3.26, for example using the Flatpak build as of commit 0ec092f400dd, is already using portals, thanks to the updated WebKitGTK+ 2.18, saving for issue #81.

[indolering]

Can we remove the "--filesystem=xdg-documents" and "--filesystem=xdg-pictures" permissions? Riot and WebKitGTK both suck in terms of security.