SE-0494: Add `isIdentical(to:)` Methods for Quick Comparisons to Concrete Types

[tera]

@Agent

The proposal mentions === but only to say that that operator is orthogonal and intended for AnyObject. But there’s obvious arguments for using it instead of isIdentical(to:).

It looks good on paper but it's not a good idea, as the feature being discussed is advanced/low level optimisation feature, the spelling for which must be more "scary" than a mere ===. I found this reasoning convincing.