Fix Issue 20087 - scope not parsed for types in template argument lists

[JinShil]

https://issues.dlang.org/show_bug.cgi?id=20087

[Geod24]

I commented on the bugzilla issue.

[JinShil]

It seems scope is a bit overloaded. When used on variables it's a storage class, but when used on parameters it's a type modifier. For some reason, scope as a type modifier is absent of any implementation, so I'm exploring what it would take, and what the consequences would be if it were implemented.