Adding Interface Blocks to glsl parser

Added code to parse interface blocks and the
corresponding layout qualifiers to the glsl parser.

Change-Id: Idfcbf08f3f877ea9641ae611e6bddd2be1ffb952
Reviewed-on: https://swiftshader-review.googlesource.com/3480
Tested-by: Alexis Hétu <sugoi@google.com>
Reviewed-by: Nicolas Capens <capn@google.com>