Diamond shouldn't be allowed in pattern

[stephan-herrmann]

From #3069 (comment):

It seems that this snippet:

if (p instanceof R<>(String a))

is actually illegal syntax.

Diamond syntax is defined in

ClassOrInterfaceTypeToInstantiate:
   {Annotation} Identifier {. {Annotation} Identifier}
   [TypeArgumentsOrDiamond]

TypeArgumentsOrDiamond:
   TypeArguments
   <>

But the instanceof rule doesn't seem to have a path into that rule, start the search from

InstanceofExpression:
   RelationalExpression instanceof ReferenceType

[stephan-herrmann]

The diamond operator was added in your grammar via 699cc35 (merge), orginally 0e08015. Unfortunately no bug with any discussion was linked. I wonder if the grammar corresponds to what specification we had at that time, or if perhaps the grammar was intentionally made more permissive, to allow for better error messages?