add bit_field parsing to core:odin/parser

Also adds it to the core type thingy like it is in the compiler.

core/odin/ast/walk.odin

@@ -414,7 +414,15 @@ walk :: proc(v: ^Visitor, node: ^Node) {
 		walk(v, n.row_count)
 		walk(v, n.column_count)
 		walk(v, n.elem)
-
+	case ^Bit_Field_Type:
+		walk(v, n.backing_type)
+		for f in n.fields {
+			walk(v, f)
+		}
+	case ^Bit_Field_Field:
+		walk(v, n.name)
+		walk(v, n.type)
+		walk(v, n.bit_size)
 	case:
 		fmt.panicf("ast.walk: unexpected node type %T", n)
 	}