mweststrate / immer / #1088

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fix: Add a type-checking fast path for primitive types (#755)

When `Draft<T>` is applied to a large enum type, TypeScript has to do a
lot of unnecessary structural comparisons to confirm that no element of
the enum matches `Function`, `Date`, `RegExp`, etc.  Determining that
they do match `string` or `number`, on the other hand, is trivial.  This
change splits `PrimitiveType` out of `AtomicObject` so that the fast
path can be checked first.

In https://github.com/microsoft/TypeScript/issues/42824, this cut the
check time from ~2.5 seconds to ~0.3 seconds.

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