Fix #4173: Consequest scope with the same condition

[phpstan-bot]

This PR fixes phpstan/phpstan#4173

When merging scopes from three or more branches (e.g., if/elseif/elseif/else), MutatingScope::mergeWith() performs pairwise merges. During each merge, intersectConditionalExpressions() preserves only conditional expressions that exist in both scopes. However, a conditional expression whose guard condition is impossible in the other scope is vacuously true there and should be preserved.

For example, with branches count($row) === 3 (defines $value), count($row) === 2 (no $value), and count($row) === 1 (no $value):

• After merging branches 1+2, a conditional expression "if count($row)=3 then $value is defined" is created
• When merging that result with branch 3 (count=1), intersectConditionalExpressions() discards this conditional expression because branch 3 doesn't have it
• But in branch 3, count($row) is 1, so the guard count($row)=3 can never be satisfied — the conditional expression is vacuously true
• Later, when count($row) === 1 is eliminated by an early return, the conditional expression is needed to know that $value is defined when count($row) is 2 or 3

The fix adds preserveVacuousConditionalExpressions() which recovers conditional expressions from either scope whose guard conditions are provably impossible in the other scope (using isSuperTypeOf()->no()).

Additionally fixes two pre-existing issues in PHPStan's own code that are now detected due to improved analysis precision:

• Removed a redundant $parametersAcceptor !== null check in NodeScopeResolver (always true within $methodReflection !== null block)
• Stored $operand->getMax() in a local variable in InitializerExprTypeResolver to allow proper null-narrowing