Moved some of the struct / indexing code
from glslang.y to the ParserHelper class
and prepared it for uniform blocks.

Change-Id: I2d5d380f662f36f04d74783fd542c4b258d3f3a5
Reviewed-on: https://swiftshader-review.googlesource.com/3441Tested-by: Alexis Hétu <sugoi@google.com>
Reviewed-by: Nicolas Capens <capn@google.com>