nir/linker: add gl_nir_link_uniform_blocks.c

nir/linker: add gl_nir_link_uniform_blocks.c

Adding the ability to link uniform blocks and shader storage blocks
using NIR, intended for ARB_gl_spirv support. Among other things, this
linking needs to take into account that everything should work without
names, as they could be not present, while the GLSL IR uniform block
linking was wrote with the names on its core.

The other major difference compared with the GLSL IR linker is that we
don't deal with layouts. There are no references to std140, std430,
etc. Layouts are expressed through explicit offset, array stride and
matrix stride. That simplifies how the buffer size are computed. But
also means that we couldn't use the existing methods at glsl_types, so
we needed to implement new methods.

It is worth to note that this linking do a iteration over the
glsl_types, similarly to what the linking uniforms do. A possible
future improvement would be refactor both cases to try to share more
code that it sharing right now. On GLSL IR there are a class visitor,
specialized on each case, for that sharing. As adding a class visitor
on C would more complicated, for now we are just iterating on both.

Signed-off-by: Alejandro Piñeiro <apinheiro@igalia.com>
Signed-off-by: Neil Roberts <nroberts@igalia.com>
Signed-off-by: Antia Puentes <apuentes@igalia.com>
v2: (from Timothy review)
   * Fix variable name convention
   * Stop to use _function_name convention
   * Don't use // for comments
   * "nir/linker: Keep track of the stages referencing an UBO/SSBO"
     squashed with this patch

v3: (from Caio review)
   * Don't delete the linked shader on failure
   * Use rzalloc_array to avoid some explicit initializations

Reviewed-by: Timothy Arceri <tarceri@itsqueeze.com>
Reviewed-by: Caio Marcelo de Oliveira Filho <caio.oliveira@intel.com>