Renaming UniformBufferBinding to BufferBinding

UniformBufferBinding was used for both uniform buffers
and transform feedback buffers, so the uniform buffer
specific name no longer made sense.

Change-Id: I36a5b774e780460fa090c6c611cb8cb475ef2ced
Reviewed-on: https://swiftshader-review.googlesource.com/5042
Tested-by: Alexis Hétu <sugoi@google.com>
Reviewed-by: Nicolas Capens <capn@google.com>