The `modifierFlagsCache` property is among the top properties that cause
megamorphic stub cache misses when having `tsc` build itself. This is
because it's added sort of randomly to a whole lot of different objects,
at arbitrary points after their initialization.
This also means that `modifierFlagsCache` is often not present on the
instances, which means that when missing on the megamorphic stub cache,
Node/V8 has to compute `NonExistent` handlers for the relevant inline
caches.
It's a lot cheaper to just make sure that the property is always
existent on the instance, and ideally also at the same offset. This
change ensures exactly that.
Drive-by-fix: Also make sure that `transformFlags` (and `parent`)
is always at the same offset for `Node` objects.