fix Issue 13525 - Redundant SpecialKeyword grammar listd in DefaultInitializerExpression

Remove DefaultInitializerExpression and replace with AssignExpression
Add SCRIPT macro

Andrei suggested that I add this SCRIPT macro in PR 2567 on phobos.
Merge pull request #668 from markisaa/scriptmacro

Add SCRIPT macro
Merge pull request #661 from 9rnsr/fix13525

Issue 13525 - Redundant SpecialKeyword grammar listd in DefaultInitializerExpression