RFR: 8365203: defineClass with direct buffer can cause use-after-free

[Per Minborg]

### Description
This PR proposes to update the `ClassLoader` implementation to properly guard access to the provided `ByteBuffer` when defining a class using `defineClass(String, ByteBuffer, ...)`. Specifically, calls to `SharedSecrets.getJavaNioAccess().acquireSession(ByteBuffer)` and `releaseSession(ByteBuffer)` have been introduced to ensure safe and consistent buffer access throughout the native class definition process, even in the case of a `ByteBuffer` is backed by a `MemorySegment`.

### Impact
This modification is internal to the `ClassLoader` implementation and does not affect the public API.
Improves the robustness and security of class loading from buffers.

### Testing
Tier 1, 2, and 3 JDK tests pass on multiple platforms.

-------------

Commit messages:
 - Add test
 - Update copyright year
 - Guard ClassLoader::defineClass2

Changes: https://git.openjdk.org/jdk/pull/26724/files
  Webrev: https://webrevs.openjdk.org/?repo=jdk&pr=26724&range=00
  Issue: https://bugs.openjdk.org/browse/JDK-8365203
  Stats: 88 lines in 2 files changed: 84 ins; 0 del; 4 mod
  Patch: https://git.openjdk.org/jdk/pull/26724.diff
  Fetch: git fetch https://git.openjdk.org/jdk.git pull/26724/head:pull/26724

PR: https://git.openjdk.org/jdk/pull/26724