Add direct casting type to .as reference

[Eze-Scribd]

Added a new way to add type casting to reference

It now supports type casting of two ways. Strict and Optional

For an optional type casting:
Before:

reference: .named("identifier") | .named(" as? ") | TypeIdentifier.entityRelationshipIdentifier.reference)

Now:

reference: .named("identifier") | .as(.optional(TypeIdentifier.entityRelationshipIdentifier)))

For an strict type casting:
Before:

member: .named("$0") | .as | TypeIdentifier.optional(wrapped: .entityMetadata).reference)

Now:

member: .named("$0") | .as(.strict(TypeIdentifier.optional(wrapped: .entityMetadata)))