NodeScopeResolver: Prevent repetitive union of static types

[staabm]

re-use types introduced in #4841

removes a few TypeCombinator::union calls

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since TypeCombinator::union is the slowest path we have right now, this is a great thing to have.

[phpstan-bot]

This pull request has been marked as ready for review.

[VincentLanglet]

I think name could be challenged for 3 reasons:

• Existing methods are called falsey (and truthy) and not getFalseyType.
  Should it be something like nonIntArrayKeyValue ?

• I had trouble ton understand what was IntArrayKeyValueType and nonIntArrayKeyValueType. Should another name be use ? With offset maybe ?

• nonInt is not really valid since we was using $offsetType->isInteger()->yes() for getIntArrayKeyValueType and getNonIntArrayKeyValueType in the other case, including the MAYBE case. So it's more a general case.

Maybe something like

generalOffsetAccessible()
intOffsetAccessible()