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);
+}
+
 }

lib/Channel.bux

@@ -32,6 +32,10 @@ func Channel_Free<T>(ch: *Channel<T>) {
     bux_channel_free(ch.handle);
 }
 
+func Channel_Drop<T>(ch: *Channel<T>) {
+    Channel_Free<T>(ch);
+}
+
 /* Convenience wrappers for common types */
 func Channel_SendInt(ch: *Channel<int>, value: int) {
     bux_channel_send(ch.handle, (&value) as *void);

lib/Map.bux

@@ -87,6 +87,10 @@ func Map_Free<K, V>(m: *Map<K, V>) {
     m.len = 0;
 }
 
+func Map_Drop<K, V>(m: *Map<K, V>) {
+    Map_Free<K, V>(m);
+}
+
 // ---------------------------------------------------------------------------
 // StringMap<V> — specialized Map for String keys, using strcmp
 // ---------------------------------------------------------------------------

lib/Set.bux

@@ -68,4 +68,8 @@ func Set_Free<T>(s: *Set<T>) {
     s.len = 0;
 }
 
+func Set_Drop<T>(s: *Set<T>) {
+    Set_Free<T>(s);
+}
+
 }