Add fast path to TypeCombinator::union() for trivial 2-type cases#5325

SanderMuller wants to merge 2 commits intophpstan:2.1.xphpstan/phpstan-src:2.1.xfrom

SanderMuller:perf/typecombinator-union-fast-pathSanderMuller/phpstan-src:perf/typecombinator-union-fast-pathCopy head branch name to clipboard