The basic approach is to have the batched renderer create and bind a
vertex array object if it detects we are using an OpenGL Core profile
context. The VAO is bound for the duration of the QQ2 renderer's
work cycle and unbound at the end so as to not interfere with any
other VAO's a user may wish to use.

All shaders have been copied and ported to be compliant with the
GLSL 150 core specification which is the minimum for a Core profile
context (OpenGL 3.2 Core). We are not using any newer features as
yet so this will work anywhere we can get a Core profile context.

The QSGShaderSourceBuilder class has been extended to resolve any
requests for shaders to the same basefilename with "_core"
appended prior to any file extension. This could be extended in
the future to allow version, or GPU or platform specific shaders.

The QSGShaderSourceBuilder has also been extended to allow it to
insert #define definitions in the prologue of a shader. Any such
de...