compiler: disambiguate function-local named types (#5336)

* compiler: make getTypeCodeName a method on compilerContext

* testdata: add regression tests for function-local named types

* compiler: disambiguate function-local named types

* Some PR feedback

main_test.go

@@ -76,6 +76,8 @@ func TestBuild(t *testing.T) {
 		"init_multi.go",
 		"interface.go",
 		"json.go",
+		"localtypes/",
+		"localtypes.go",
 		"map.go",
 		"map_bigkey.go",
 		"math.go",