Verify Flatpak + Update Flatpak dependencies

[MMachado05]

Currently, despite the flatpak having come about by a discussion with the primary developer of Revolt, the flatpak is listed as "unverified" on Flathub. This means it's considered less safe by the (somewhat misguided) Flathub security guidelines, and will not appear by default on distros like Linux Mint, which have unverified flatpaks disabled by default.

Secondly, and perhaps this may be better suited for the manifest repo, the current flatpak is dependent on various end-of-life runtimes, those being org.freedesktop.Platform//22.08 and its derivatives:

• org.freedesktop.Platform.GL.default//22.08
• org.freedesktop.Platform.GL.default//22.08-extra
• org.freedesktop.Platform.GL.Locale//22.08
• org.freedesktop.Platform.GL.Intel//22.08

Beyond introducing potential security concerns, this also creates various warnings when updating flatpaks on the system.