The EGL path had no support for presenting sub-regions of the screen, we can
leverage EGL_NV_post_sub_buffer for that. This wouldn't be a win if we didn't
have to opt-out of flipping.
REVIEW: 102889
Second part of cleaning up the lib directory: the effects library
now lives in libkwineffects/ directory.
For existing effects nothing changes as the install path is unchanged.
The change obsoletes the lib/ directory.
As glplatform.h has not yet been exported I dared to export it and
adjust the places where it is used.
CCMAIL: kwin@kde.org
