Faster ObjectType->getEnumCases() type substraction

[staabm]

turns a nested loop into 2 subsequent loops.

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repro of phpstan/phpstan#11263

before this PR (c6b961d)

time php bin/phpstan analyze slow.php --debug
 8.52s user 0.14s system 99% cpu 8.732 total
time php bin/phpstan analyze slow.php --debug
 8.44s user 0.15s system 99% cpu 8.624 total

after this PR

time php bin/phpstan analyze slow.php --debug
 7.83s user 0.14s system 99% cpu 8.010 total
time php bin/phpstan analyze slow.php --debug
 7.80s user 0.14s system 99% cpu 7.979 total

[ondrejmirtes]

Thank you.

[thg2k]

There is a typo in the local variable name subtracedEnumCaseNames

[ondrejmirtes]

@thg2k Please send a PR.