intel/compiler: Implement Task Output and Mesh Input

Implement the output written by the task *workgroup* and available to
all the mesh *workgroups* dispatched from that task.  We currently
ignore any layout annotations (since they are not really testable) and
produce a (packed) layout ourselves.

The URB messages are only SIMD8, so for larger SIMDs, the functions
will produce multiple messages.  Making this lowering here instead of
the generic lower_simd_width() since it is not just a matter of
zip/unzip, e.g. the offset must be adjusted.

Indirect writes/reads are implemented by handling one component at a
time and using the PER_SLOT variant of the messages.

Note that VK_NV_mesh_shader allows reading outputs, so add support for
that as well.

Reviewed-by: Lionel Landwerlin <lionel.g.landwerlin@intel.com>
Part-of: <https://gitlab.freedesktop.org/mesa/mesa/-/merge_requests/13661>

src/intel/compiler/brw_fs.h

@@ -329,6 +329,11 @@ public:
    void emit_cs_terminate();
    fs_reg *emit_work_group_id_setup();
 
+   void emit_task_mesh_store(const brw::fs_builder &bld,
+                             nir_intrinsic_instr *instr);
+   void emit_task_mesh_load(const brw::fs_builder &bld,
+                            nir_intrinsic_instr *instr);
+
    void emit_barrier();
 
    void emit_shader_time_begin();