glsl: store ubo or ssbo index in block index

glsl: store ubo or ssbo index in block index

Previously we store the buffer block index i.e the index of a combined
ubo/ssbo list.

Fixes several dEQP-GLES31.functional tests:
- program_interface_query.uniform.block_index.block_array
- program_interface_query.uniform.block_index.named_block
- program_interface_query.uniform.block_index.unnamed_block
- program_interface_query.uniform.random.10
- program_interface_query.uniform.random.15
- program_interface_query.uniform.random.22
- program_interface_query.uniform.random.24
- program_interface_query.uniform.random.26
- program_interface_query.uniform.random.28
- program_interface_query.uniform.random.3
- program_interface_query.uniform.random.31
- program_interface_query.uniform.random.38
- program_interface_query.uniform.random.5

Bugzilla: https://bugs.freedesktop.org/show_bug.cgi?id=94116
Reviewed-by: Kenneth Graunke <kenneth@whitecape.org>