RFR: 8325949: Create an internal utility method for creating VarHandle instances

[Per Minborg]

This PR suggests introducing an internal class in `java.base` to simplify the use of some `MethodHandles.Lookup` operations.

While the utility of the methods might appear to be limited in classes with many static `VarHandle`/`MethodHandle` variables, it should be noted that the class files become smaller and simpler. Here are some examples:

| Class File                                      | Base [Bytes] | Patch [Byte] |
| --------------------------------| ------------- | ------------ |
| FutureTask.class                          |             10255 |           10154 |
| AtomicBoolean.class                   |              5364 |             5161 |
|AtomicMarkableReference.class |              3890 |            3687 |

![image](https://github.com/user-attachments/assets/fdcbbdfe-c906-4e50-a48c-4944c53c08cc)

The new `MethodHandlesInternal.class` file is of size 2012 bytes.

In total for `java.base` we have:

| Build map "jdk"  | Size [Bytes] |
| ---------------| ------------- |
| Base                 |        5963657 |
| Patch                |        5962751 |
| Delta                 |                906|

For 60 billion instances, this represents 54 TB.

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

Commit messages:
 - Fix copyright headers
 - Introduce MethodHandlesInternal

Changes: https://git.openjdk.org/jdk/pull/20972/files
  Webrev: https://webrevs.openjdk.org/?repo=jdk&pr=20972&range=00
  Issue: https://bugs.openjdk.org/browse/JDK-8325949
  Stats: 423 lines in 31 files changed: 109 ins; 202 del; 112 mod
  Patch: https://git.openjdk.org/jdk/pull/20972.diff
  Fetch: git fetch https://git.openjdk.org/jdk.git pull/20972/head:pull/20972

PR: https://git.openjdk.org/jdk/pull/20972