glsl: mark variables produced by lower_named_interface_blocks.

These variables will need to be treated specially by
program_resource_visitor, so that they can be addressed through the
API using their interface block name (and array index, for interface
block arrays).
glsl: Account for interface block lowering in program_resource_visitor.

When program_resource_visitor visits variables that were created by
lower_named_interface_blocks, it needs to do extra work to un-do the
effects of lower_named_interface_blocks and construct the proper API
names.

Fixes piglit test
spec/glsl-1.50/execution/interface-blocks-api-access-members.