compiler: Fixed missing struct declarator in MkDeclaration()
- This solves the crash reported by Redj on Git markers in FindInFilesDialog.ec
- Also fixed the problems in 2 other ways:
   * Detecting a bit class becoming a non-bit class
   * Struct declarator check in firstPass.ec
- Fixed memory leak in debug mode by freeing ModuleImports after freeing AST in CodeEditor