RFR: 8314684: Add overview docs to loaderConstraints.cpp [v2]

[Ioi Lam]

> I added some documentation to make it easier to understand loaderConstraints.cpp. Please review and check if my description is actually correct. Thanks!

Ioi Lam has updated the pull request incrementally with one additional commit since the last revision:

  @calvinccheung comments

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Changes:
  - all: https://git.openjdk.org/jdk/pull/15372/files
  - new: https://git.openjdk.org/jdk/pull/15372/files/bfd5c00e..557eafa3

Webrevs:
 - full: https://webrevs.openjdk.org/?repo=jdk&pr=15372&range=01
 - incr: https://webrevs.openjdk.org/?repo=jdk&pr=15372&range=00-01

  Stats: 7 lines in 1 file changed: 0 ins; 0 del; 7 mod
  Patch: https://git.openjdk.org/jdk/pull/15372.diff
  Fetch: git fetch https://git.openjdk.org/jdk.git pull/15372/head:pull/15372

PR: https://git.openjdk.org/jdk/pull/15372