compiler, reflect: add map key and element type info

src/reflect/type.go

@@ -33,6 +33,8 @@
 // - map types (this is still missing the key and element types)
 //     meta         uint8
 //     ptrTo        *typeStruct
+//     elem         *typeStruct
+//     key          *typeStruct
 // - struct types (see structType):
 //     meta         uint8
 //     numField     uint16
@@ -408,6 +410,13 @@ type arrayType struct {
 	arrayLen uintptr
 }
 
+type mapType struct {
+	rawType
+	ptrTo *rawType
+	elem  *rawType
+	key   *rawType
+}
+
 // Type for struct types. The numField value is intentionally put before ptrTo
 // for better struct packing on 32-bit and 64-bit architectures. On these
 // architectures, the ptrTo field still has the same offset as in all the other