Also rename test/language/expressions/dynamic-import/assignment-expression/

- Add cases for invalid syntax
- Add valid cases
- nested imports
- add non existent file case
- Fix cases and templates to use a full importcall expr token
- add case for call expression position
- remove unnecessary module flag from templates
- Add templates for nested with

Implementation Contributions: Creating initial empty dir for receiving "upstreamed" test material via automaton

This script is intended to identify common test file formatting errors
prior to their acceptance into the project. It is designed to support
future extensions for additional validation rules.