[platformsupport] Minor code style and class variables access changes
Summary:
Some of these variables have been declared protected but can apparently
also be private.
Other minor code style improvements.
Test Plan: Compiles, Wayland nested session runs.
Reviewers: KWin, zzag
Reviewed By: KWin, zzag
Subscribers: zzag, kwin
Tags: KWin
Differential Revision: https://phabricator.kde.org/D22109