Refactoring codegen with Flat / Lowered types. Helpers for struct gep. type_get_indexed_type no longer returns the canonical type, fixes issues in #2534

test/test_suite/define/alias_through_index.c3

@@ -0,0 +1,7 @@
+alias MyChar = char;
+
+fn void main()
+{
+	MyChar[<2>] my = { '1', '2' };
+	my[0].ok(); // #error: There is no member or method 'ok' on 'MyChar' (char)
+}