selfhost: add *_Drop wrappers to stdlib types; auto-drop uses _Drop instead of _Free

- Array.bux, Channel.bux, Set.bux, Map.bux: add *_Drop<T> delegating to *_Free
- hir_lower.bux: Lcx_BuildAutoDropFree searches for _Drop suffix instead of _Free
- Skip direct lowering of generic functions (only monomorphized instances)

lib/Array.bux

@@ -46,4 +46,8 @@ func Array_Free<T>(self: *Array<T>) {
     self.cap = 0;
 }
 
+func Array_Drop<T>(self: *Array<T>) {
+    Array_Free<T>(self);
+}
+
 }