[Parser] Improve diagnostics for generic parameter list in enum cases

[mininny]

enum Foo {
    case bar<T>(baz: T)
            ^
}

above code results in

Consecutive declarations on a line must be separated by ';'
Expected declaration

which is not very helpful for informing the user that generics are not available as a case in enums.

Something like enum cases cannot have generic parameters. did you mean to attach it to enum declaration could be emitted for better guidance to the users.

Resolves #69036

[AnthonyLatsis]

Closed in favor of #69055.