RFR: 8200559: Java agents doing instrumentation need a means to define auxilary classes

[Rafael Winterhalter]

To allow agents the definition of auxiliary classes, an API is needed to allow this. Currently, this is often achieved by using `sun.misc.Unsafe` or `jdk.internal.misc.Unsafe` ever since the `defineClass` method was removed from `sun.misc.Unsafe`.

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

Commit messages:
 - 8200559: Java agents doing instrumentation need a means to define auxiliary classes

Changes: https://git.openjdk.java.net/jdk/pull/3546/files
 Webrev: https://webrevs.openjdk.java.net/?repo=jdk&pr=3546&range=00
  Issue: https://bugs.openjdk.java.net/browse/JDK-8200559
  Stats: 185 lines in 4 files changed: 185 ins; 0 del; 0 mod
  Patch: https://git.openjdk.java.net/jdk/pull/3546.diff
  Fetch: git fetch https://git.openjdk.java.net/jdk pull/3546/head:pull/3546

PR: https://git.openjdk.java.net/jdk/pull/3546