[CodeQuality] Extract NullableObjectToInstanceofFactory shared by nullable-object instanceof rules

[TomasVotruba]

Four rules independently built the same $expr instanceof X node from a nullable ObjectType, each with its own private helper:

• ObjectExplicitBoolCompareRector - resolveNullable()
• FlipTypeControlToUseExclusiveTypeRector - processConvertToExclusiveType()
• BinaryOpNullableToInstanceofRector - createExprInstanceof()
• WhileNullableToInstanceofRector - createInstanceof()

This extracts the shared node construction into NullableObjectToInstanceofFactory::create(Expr, ObjectType, bool $isNegated) and migrates all four rules to it. The factory keeps the ShortenedObjectType/AliasedObjectType FQCN handling from FlipTypeControl - the other callers never hit those branches, so behavior is unchanged.

Only node construction is shared. Each rule keeps its own type-resolution path (nodeTypeResolver, nullableTypeAnalyzer, native scope type), since those differ in depth and source and are sensitive to resolution order.

EmptyOnNullableObjectToInstanceOfRector is intentionally left out - it maps the type through StaticTypeMapper to a Name rather than building a FullyQualified from the class name.

Rules stay separate on purpose: they match different input idioms (!$item, $item === null, &&/||, while) and converge on the same output.

No behavior change. Fixtures untouched, all pass.