Fix go generator undefined Package name, also throwing exception (#7632)

* Fix go generator undefined Package, also throw exception in specific examples.

* Add test for go generator import problem

* Add new version of generated go file. Fix conflict.

* Add executable permission to generate_code.py script.

* Improve test quality, remove unwanted generated files, better naming

* Fix comments

* clang format

Co-authored-by: Derek Bailey <derekbailey@google.com>

tests/include_test/sub/no_namespace.fbs

@@ -0,0 +1,3 @@
+table Pizza {
+  size: int;
+}