This cl adds validation that uniform block instance names aren't
reserved names.

Fixes 2 tests:
dEQP-GLES3.functional.shaders.uniform_block.invalid.invalid_identifier_instance_name_*

Change-Id: I4a39c734cdf4d11ea4221c73c1f639fa2f56921d
Reviewed-on: https://swiftshader-review.googlesource.com/15868Tested-by: Alexis Hétu <sugoi@google.com>
Reviewed-by: Nicolas Capens <nicolascapens@google.com>