Make multisampling more robust in QOpenGLFramebufferObject

Some drivers are reported to get confused when passing different
sample counts (requested vs. actual) to the color and depth/stencil
attachments. To overcome this, pass the requested sample count to all
the attachments.

Task-number: QTBUG-33406
Change-Id: I17b0e3dbbd78de2ab0f45e95164b4f326d47aeff
Reviewed-by: Paul Olav Tvete <paul.tvete@digia.com>
Reviewed-by: Kimmo Leppälä <kimmo.leppala@digia.com>
Avoid polluting the output with warnings on eglfs

Many windowing functions are not supported (since they do not make sense)
on the embedded platforms. Provide empty implementations for a few more
to avoid showing useless warnings, in particular for widget apps. The
user cannot do anything about it and these are not errors.

Task-number: QTBUG-39081
Change-Id: I29afd981e037d1e6772bcdfc33497e6d0ae02008
Reviewed-by: Paul Olav Tvete <paul.tvete@digia.com>
Fix visual selection with EGL on xcb

Using a 24-bit visual for 8888 configs is wrong since we loose the
alpha channel. This breaks translucent windows and, among others,
leads to not showing drag pixmaps (that typically have transparent
areas) properly.

Change-Id: I516c84327680b76996b622831e431c29d840471e
Task-number: QTBUG-35126
Reviewed-by: Paul Olav Tvete <paul.tvete@digia.com>
Fix alpha in no-opengl configuration on xcb

Like the EGL + xcb configuration, the -no-opengl is broken too when
it comes to translucent windows: Requesting an alpha channel is futile
since the xcb_create_window call always uses the root's depth and visual.

This is now corrected by picking a 32-bit visual.

This will make translucent windows and drag pixmaps appear correctly again.

Task-number: QTBUG-35126
Change-Id: I00e7d6e08b5fcc055ef3ea6d822561740a1f5457
Reviewed-by: Gatis Paeglis <gatis.paeglis@digia.com>