RFR: 8328679: Improve comment for UNSAFE_ENTRY_SCOPED in unsafe.cpp [v2]

[Maurizio Cimadamore]

> This small PR is an attempt at improving the comment in the UNSAFE_ENTRY_SCOPED macro.
> I found that the comment contained some duplicated claims, did not properly introduced the concepts it referred to, and some of its claims were not explained in full.
> 
> As this is a delicate part of how FFM ensures the "no use after free" guarantee, I think it would be a good idea for this comment to better reflect what the expectations are.

Maurizio Cimadamore has updated the pull request incrementally with one additional commit since the last revision:

  Update src/hotspot/share/prims/unsafe.cpp
  
  Co-authored-by: Jorn Vernee <JornVernee at users.noreply.github.com>

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

Changes:
  - all: https://git.openjdk.org/jdk/pull/18429/files
  - new: https://git.openjdk.org/jdk/pull/18429/files/42e8c416..1f1c0684

Webrevs:
 - full: https://webrevs.openjdk.org/?repo=jdk&pr=18429&range=01
 - incr: https://webrevs.openjdk.org/?repo=jdk&pr=18429&range=00-01

  Stats: 1 line in 1 file changed: 0 ins; 0 del; 1 mod
  Patch: https://git.openjdk.org/jdk/pull/18429.diff
  Fetch: git fetch https://git.openjdk.org/jdk.git pull/18429/head:pull/18429

PR: https://git.openjdk.org/jdk/pull/18429