RFR: 8343439: [JVMCI] Fix javadoc of Services.getSavedProperties

[Doug Simon]

The javadoc of `jdk.vm.ci.services.Services.getSavedProperties` is currently:

    /**
     * Gets an unmodifiable copy of the system properties parsed by {@code arguments.cpp}
     * plus {@code java.specification.version}, {@code os.name} and {@code os.arch}.
     * The latter two are forced to be the real OS and architecture. That is, values
     * for these two properties set on the command line are ignored.
     */

The details about how the copy is initialized are specific to the HotSpot VM. On SVM, the semantics can be different. This PR separates out the HotSpot specific part.

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Commit messages:
 - separate out HotSpot specific semantics of getSavedProperties

Changes: https://git.openjdk.org/jdk/pull/21832/files
  Webrev: https://webrevs.openjdk.org/?repo=jdk&pr=21832&range=00
  Issue: https://bugs.openjdk.org/browse/JDK-8343439
  Stats: 6 lines in 1 file changed: 2 ins; 0 del; 4 mod
  Patch: https://git.openjdk.org/jdk/pull/21832.diff
  Fetch: git fetch https://git.openjdk.org/jdk.git pull/21832/head:pull/21832

PR: https://git.openjdk.org/jdk/pull/21832