RFR: 8279993: Assert that a shared class is not loaded more than once [v2]

[Calvin Cheung]

> Please review this small fix for adding a debug only counter `InstanceKlass::_shared_class_load_count` to ensure a shared class is loaded only once.
> 
> Passed tiers 1,2,3 testing.

Calvin Cheung has updated the pull request incrementally with one additional commit since the last revision:

  use Atomic::add to increment the field

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Changes:
  - all: https://git.openjdk.org/jdk/pull/14023/files
  - new: https://git.openjdk.org/jdk/pull/14023/files/9d5f70ca..5f3dff93

Webrevs:
 - full: https://webrevs.openjdk.org/?repo=jdk&pr=14023&range=01
 - incr: https://webrevs.openjdk.org/?repo=jdk&pr=14023&range=00-01

  Stats: 4 lines in 2 files changed: 1 ins; 1 del; 2 mod
  Patch: https://git.openjdk.org/jdk/pull/14023.diff
  Fetch: git fetch https://git.openjdk.org/jdk.git pull/14023/head:pull/14023

PR: https://git.openjdk.org/jdk/pull/14023