#4034 Cache Type instances in TypeFactory.getType(...) to avoid redundant work - #4129

Fixes #4034.

Background & Motivation

In MapStruct's annotation processor, TypeFactory.getType(...) is invoked frequently across rounds and model element processors (mapping methods, source/target property resolution, accessor discovery, enclosing element inspection). Previously, TypeFactory instantiated a fresh Type object on nearly every invocation:

• This caused repetitive enclosing-element traversals, member lookups, and typeUtils.isSubtypeErased(...) checks.
• Per-Type memoized caches (such as isNullMarked(), accessors, and method lists) were repeatedly re-allocated or re-queried instead of shared.

Solution

1. Round-Scoped Type Element Cache:
   • Added typeElementCache (IdentityHashMap<TypeElement, Type>) in TypeFactory to intern prototypical types derived directly from non-generic TypeElement instances.
2. Structural Type Mirror Cache:
   • Added typeCache (HashMap<TypeCacheKey, Type>) using an immutable structural fingerprint (TypeFingerprint) that safely distinguishes:
     • Declared types (interned by qualified name / canonical TypeElement, type argument fingerprints, and enclosing type fingerprint).
     • Array types (by component type fingerprint).
     • Wildcard types (by extends / super bound fingerprints).
     • Type variables (by name and upper bound fingerprints).
     • Primitive and void types (by TypeKind).
   • The cache key strictly distinguishes contextual configuration flags: isLiteral and alwaysImport.
3. Safety & Erroneous Types:
   • Pre-validation check canBeProcessed(mirror) ensures erroneous/unresolvable types are never cached or suppressed, preserving TypeHierarchyErroneousException semantics.
4. Testing:
   • Added Issue4034Test and Issue4034Mapper verifying that identical Type instances are returned for repeated lookups (getType(TypeElement), getType(TypeMirror), generic List<String>), differing type arguments (List<String> vs List<Integer>) produce distinct instances, and flag variants (isLiteral, alwaysImport) remain distinct.
   • All tests pass and checkstyle audit passes with 0 violations.