Optimize GL emulation prepareClientAttributes. Fix issues where the slow path was not able to handle unaligned source data. Annotate some unsupported cases. Remove liveClientAttributes, which does not seem to be a win in profiles.
Reintroduce liveClientAttributes to optimize the case where GL emulation code is called with a very large GLImmediate.MAX_TEXTURES size.
Merge pull request #1999 from juj/gl_prepareclientattr

GL prepareClientAttributes.