Minor enhancement suggestion

---
template BasicTypeUDA(T)
{
    @T(0) int v1;
    @int(0) int v2; // not accepted by the parser but this is the same as v1 attribute when  `T` is an `int`.
}

alias WithInt = BasicTypeUDA!int;
---

possible by simplifying the current rule for UDA this way:

UserDefinedAttribute:
    @ ( ArgumentList )
-    @ Identifier
-    @ Identifier ( ArgumentListopt )
-    @ TemplateInstance
-    @ TemplateInstance ( ArgumentListopt )
+    @ BasicType
+    @ BasicType ( ArgumentListopt )

since BasicType covers Identifier, TemplateInstance, builtin types and even more. (https://dlang.org/spec/declaration.html#BasicType)

The @ guarantees that parsing will not become ambiguous.
This would simplify a bit the language by generalizing the use of the construction syntax, although we all know that `@Type(args)` is just the short for `@(Type(args))`.