Fix core context creation in GdkGLContext

Fix core context creation in GdkGLContext

- Specifically request GL version when creating context. Just specifying core
profile bit results in the requested version defaulting to 1.0 which causes
the core profile bit to be ignored and an arbitrary compatability context to be
returned.

- Fix GL painting by removing GL calls that have been depricated by the 3.2 core
profile.

- Additionally remove glInvalidateFramebuffer() call, it is not supported by 3.2
core.

https://bugzilla.gnome.org/show_bug.cgi?id=742953