Summary
-------

Update the java.util.concurrent.ThreadLocalRandom to be a final class.

Problem
-------
The ThreadLocalRandom class has a sole private constructor:
```
private ThreadLocalRandom() {
...
```
So in essence, the ThreadLocalRandom class cannot have any sub class. Marking the ThreadLocalRandom as final would thus convey it more clearly that the class cannot be extended.


Solution
--------
Update the class to `final`.


Specification
-------------
The proposed change looks as follows:

```
--- a/src/java.base/share/classes/java/util/concurrent/ThreadLocalRandom.java
+++ b/src/java.base/share/classes/java/util/concurrent/ThreadLocalRandom.java
@@ -93,7 +93,7 @@ import jdk.internal.misc.VM;
...
-public class ThreadLocalRandom extends Random {
+public final class ThreadLocalRandom extends Random {
```