RFR: 8324514: ClassLoaderData::print_on should print address of class loader [v2]

[Aleksey Shipilev]

> This looks like a simple diagnostic regression from [JDK-8201556](https://bugs.openjdk.org/browse/JDK-8201556). Instead of printing the address of the `OopHandle` slot, we really want to print the address of the classloader that handle holds. That was not intentional, right, @coleenp?
> 
> I think we can `peek()` into handle, but the whole reason for [JDK-8201556](https://bugs.openjdk.org/browse/JDK-8201556) seems to avoid touching the classloader oops when unloading, and `peek()` would do a GC barrier on it. So, I opted to just print there is no oop on `unloading` path.

Aleksey Shipilev has updated the pull request incrementally with one additional commit since the last revision:

  Handle unloading properly

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

Changes:
  - all: https://git.openjdk.org/jdk/pull/17534/files
  - new: https://git.openjdk.org/jdk/pull/17534/files/b659c520..bbe49f09

Webrevs:
 - full: https://webrevs.openjdk.org/?repo=jdk&pr=17534&range=01
 - incr: https://webrevs.openjdk.org/?repo=jdk&pr=17534&range=00-01

  Stats: 5 lines in 1 file changed: 4 ins; 0 del; 1 mod
  Patch: https://git.openjdk.org/jdk/pull/17534.diff
  Fetch: git fetch https://git.openjdk.org/jdk.git pull/17534/head:pull/17534

PR: https://git.openjdk.org/jdk/pull/17534