intel/compiler: add a new pass to lower shading rate into HW format

Rework:
 * Jason: Modernize brw_nir_lower_shading_rate_output:
   1. Use nir_shader_instructions_pass()
   2. Use *_imm builder helpers.
   3. Use nir_intrinsic_base() instead of ->const_index[0]

v2: Also lower loads (Caio)

v3: Update stage check to trigger lowering (Caio)

v4: Assert on != MESH (Caio)

v5: Fixup instruction insertion (Caio)

Signed-off-by: Lionel Landwerlin <lionel.g.landwerlin@intel.com>
Reviewed-by: Caio Oliveira <caio.oliveira@intel.com>
Part-of: <https://gitlab.freedesktop.org/mesa/mesa/-/merge_requests/13739>

src/compiler/shader_enums.h

@@ -98,6 +98,19 @@ gl_shader_stage_is_callable(gl_shader_stage stage)
           stage == MESA_SHADER_CALLABLE;
 }
 
+static inline bool
+gl_shader_stage_can_set_fragment_shading_rate(gl_shader_stage stage)
+{
+   /* According to EXT_fragment_shading_rate :
+    *
+    *    "This extension adds support for setting the fragment shading rate
+    *     for a primitive in vertex, geometry, and mesh shading stages"
+    */
+   return stage == MESA_SHADER_VERTEX ||
+          stage == MESA_SHADER_GEOMETRY ||
+          stage == MESA_SHADER_MESH;
+}
+
 /**
  * Number of STATE_* values we need to address any GL state.
  * Used to dimension arrays.