Move resolving glxSwapIntervalMesa into platform plugin
Summary:
No need to resolve glx methods through the shared lib. At the moment
this duplicates some code, but will be cleaned up with a follow up
change.
Reviewers: KWin, Plasma on Wayland
Subscribers: plasma-devel, kwin
Tags: Plasma on Wayland, KWin
Differential Revision: https://phabricator.kde.org/D3335