RFR: 8344560: Add system property for patched runtime [v2]

[Severin Gehwolf]

> Please review this simple patch which adds a new external system property `jdk.patched` when the runtime has been patched with the `--patch-module` switch. This is useful for two reasons: 1) it allows one to determine at run-time whether or not `--patch-module` has been used (by querying the said property) 2) allows tools, such as `jlink` doing the same without needing to expose internal properties the JVM sets on initialization.
> 
> Testing:
> 
> - [x] GHA (includes new test)
> - [x] New jtreg test 
> 
> Thoughts?

Severin Gehwolf has updated the pull request incrementally with two additional commits since the last revision:

 - Set the property to false for unpatched, expand tests
 - Move and amend test

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

Changes:
  - all: https://git.openjdk.org/jdk/pull/22277/files
  - new: https://git.openjdk.org/jdk/pull/22277/files/1d2395f3..c635fdc0

Webrevs:
 - full: https://webrevs.openjdk.org/?repo=jdk&pr=22277&range=01
 - incr: https://webrevs.openjdk.org/?repo=jdk&pr=22277&range=00-01

  Stats: 198 lines in 4 files changed: 118 ins; 79 del; 1 mod
  Patch: https://git.openjdk.org/jdk/pull/22277.diff
  Fetch: git fetch https://git.openjdk.org/jdk.git pull/22277/head:pull/22277

PR: https://git.openjdk.org/jdk/pull/22277