More operators inside `is(...)` expressions

[Dennis]

On Sunday, 23 August 2020 at 21:20:21 UTC, Steven Schveighoffer 
wrote:
> What is the cost here? Just use the same AST node for the is 
> expression, and wrap it in a `not` AST node.

What would `is(int != T, T)` mean? To me it sounds like T should 
be bound to an arbitrary type that's not int, but when you lower 
it to `!is(int == T, T)` it returns false.