Fix a `shrink(map[T]U)` bug in the core lib

Fixed this error from `core:runtime`:
```odin
odin/core/runtime/core_builtin.odin(387:3) Error: Expected 2 return values, got 1 (Allocator_Error)
        return map_shrink_dynamic((^Raw_Map)(m), map_info(T), loc)
        ^~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~^
```

core/runtime/dynamic_map_internal.odin

@@ -629,7 +629,7 @@ map_reserve_dynamic :: proc "odin" (#no_alias m: ^Raw_Map, #no_alias info: ^Map_
 
 
 @(require_results)
-map_shrink_dynamic :: proc "odin" (#no_alias m: ^Raw_Map, #no_alias info: ^Map_Info, loc := #caller_location) -> Allocator_Error {
+map_shrink_dynamic :: proc "odin" (#no_alias m: ^Raw_Map, #no_alias info: ^Map_Info, loc := #caller_location) -> (did_shrink: bool, err: Allocator_Error) {
 	if m.allocator.procedure == nil {
 		m.allocator = context.allocator
 	}
@@ -639,7 +639,7 @@ map_shrink_dynamic :: proc "odin" (#no_alias m: ^Raw_Map, #no_alias info: ^Map_I
 	// map needs to be within the max load factor.
 	log2_capacity := map_log2_cap(m^)
 	if uintptr(m.len) >= map_load_factor(log2_capacity - 1) {
-		return nil
+		return false, nil
 	}
 
 	shrunk := map_alloc_dynamic(info, log2_capacity - 1, m.allocator) or_return
@@ -672,7 +672,7 @@ map_shrink_dynamic :: proc "odin" (#no_alias m: ^Raw_Map, #no_alias info: ^Map_I
 
 	map_free_dynamic(m^, info, loc) or_return
 	m.data = shrunk.data
-	return nil
+	return true, nil
 }
 
 @(require_results)