Fix #6385: updates of non-public records (with cached accessors) - #6403

Re-creates #6389 (by @wozhenbang2004, whose commits are retained) with two additions: release notes and caching of Record accessors. Fixes #6385.

Problem

readerForUpdating() on a non-public Record fails with DatabindException (access error), even though the same mapper deserializes that Record normally: the update path invokes Record component accessors reflectively without making them accessible. A public accessor of a non-public class still fails the access check.

Changes

• Fix access of Record component accessors in BeanDeserializer._deserializeRecordForUpdate(), using ClassUtil.checkAndFixAccess() subject to MapperFeature.CAN_OVERRIDE_ACCESS_MODIFIERS / OVERRIDE_PUBLIC_ACCESS_MODIFIERS (as with other call sites).
• Resolve accessors (getRecordComponents() + access fix) lazily, once per deserializer, caching them in a volatile transient Method[], instead of on every update call. A race between threads is benign (same result); both settings are mapper-level so resolving with the first DeserializationContext is safe.
• Regression test (non-public record, OVERRIDE_PUBLIC_ACCESS_MODIFIERS disabled), including a second update via the cached accessors.
• Release notes (VERSION, CREDITS).

Validation

• New test fails without the fix (cannot access a member of class ...$NonPublicRecord with modifiers "public"), passes with it.
• Full ./mvnw test: 7755 tests, 0 failures.

Fixes #6385