Add looks_switchbackdroptoandwait to compat layer

src/compiler/compat-blocks.js

@@ -8,6 +8,7 @@ const stacked = [
     'control_clear_counter',
     'control_get_counter',
     'control_incr_counter',
+    'looks_switchbackdroptoandwait',
     'looks_changeeffectby',
     'looks_nextbackdrop',
     'looks_nextcostume',