nir/lower_io: Add "explicit" IO lowering

This new pass is for lowering explicitly laid out memory coming in from
SPIR-V or a similar source.  It's quite a bit more complicated than the
normal lower_io because we have to be able to handle matrices.  The
way the stride information is stored for matrices is awkward and dealing
with row-major matrices is especially painful.

Reviewed-by: Alejandro Piñeiro <apinheiro@igalia.com>
Reviewed-by: Caio Marcelo de Oliveira Filho <caio.oliveira@intel.com>

src/compiler/nir/nir.h

@@ -2896,6 +2896,18 @@ bool nir_lower_io(nir_shader *shader,
                   nir_variable_mode modes,
                   int (*type_size)(const struct glsl_type *),
                   nir_lower_io_options);
+
+typedef enum {
+   /**
+    * An address format which is comprised of a vec2 where the first
+    * component is a vulkan descriptor index and the second is an offset.
+    */
+   nir_address_format_vk_index_offset,
+} nir_address_format;
+bool nir_lower_explicit_io(nir_shader *shader,
+                           nir_variable_mode modes,
+                           nir_address_format);
+
 nir_src *nir_get_io_offset_src(nir_intrinsic_instr *instr);
 nir_src *nir_get_io_vertex_index_src(nir_intrinsic_instr *instr);