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