IntersectionType: Prevent duplicate work in isOffsetAccessible()

[staabm]

~29% faster in phpstan/phpstan#14319

---

after this change we are not yet fast, but its a low hanging fruit along the way

[VincentLanglet]

I wonder @staabm

• If this strategy should be done for some other methods of the IntersectionType ? (We could easily do all the TrinaryLogic methods with a refactor)
• Why it's only memoized on IntersectionType (should some other type memoize too ? Either just UnionType which seems similar to Intersection or even all the types....)
• Should we have a general memoize strategy with a trait ?

WDYT ?

[staabm]

this small fix was guided by a blackfire profile which showed this slow path.
I usually add this caching only after we have evidence - and a real world case - that it is slow.

I did not change anything else, because this minimal fix was enough to get the case at hand faster.
IMO adding caching without the proof of a slow path makes things more complex, and might lead to copy/paste of caching into even more layers without a need for it.

profile before this FIX was