Switch ui/mesa to overlay convention

.orchestra/config/components.yml

 #@ load("@ytt:template", "template")
 #@ load("@ytt:data", "data")
 
-#@ load("/components/ui/mesa.lib.yml", "mesa_component")
 #@ load("/components/ui/libglvnd.lib.yml", "libglvnd_component")
 
 #@ load("/components/toolchain/arch/host.lib.yml", "host_toolchain_components")
@@ -19,7 +18,6 @@
 
 #@ load("/global_options.lib.yml", "options")
 components:
-  ui/mesa: #@ mesa_component
   ui/libglvnd: #@ libglvnd_component
 
   _: #@ template.replace(host_toolchain_components)

.orchestra/config/components/ui/mesa.lib.yml → .orchestra/config/components/ui/mesa.yml

+#@ load("@ytt:overlay", "overlay")
 #@ load("/lib/create_component.lib.yml", "single_build_component")
 
 #@ load("/global_options.lib.yml", "options")
@@ -67,5 +68,8 @@ dependencies:
   - toolchain/host/gcc
 #@ end
 
+#@overlay/match by=overlay.all, expects=1
+#@overlay/match-child-defaults missing_ok=True
 ---
-#@ mesa_component = single_build_component(**_mesa_args())
+components:
+  ui/mesa: #@ single_build_component(**_mesa_args())