Check the subtracted type when a subtracted mixed accepts a value

[zonuexe]

Closes phpstan/phpstan#15033

MixedType::accepts (and StrictMixedType, reached once RuleLevelHelper rewrites an explicit MixedType for checkExplicitMixed) accepted every value unconditionally, so a subtracted mixed like non-empty-mixed rejected nothing at argument or return boundaries, even though the same subtraction already powered narrowing and reachability (identical.alwaysFalse, if.alwaysTrue, etc.).

Acceptance now turns to No only on a definite hit (subtractedType->isSuperTypeOf($given)->yes()), so partial overlaps (e.g. a general string into non-empty-mixed, which may or may not be '') stay accepted — this preserves mixed's usual looseness and is why the fix isn't isSuperTypeOf(...)->toAcceptsResult(). NeverType is exempted, mirroring MixedType::isSuperTypeOf.

RuleLevelHelper::transformCommonType now carries the subtraction through when it converts an explicit MixedType into StrictMixedType, instead of discarding it — otherwise level max stayed silent even with MixedType fixed. VerbosityLevel::getRecommendedLevelByType escalates to precise() when a subtracted (Strict)MixedType is involved, so messages render the subtraction instead of a bare, uninformative mixed.