RFR: 8324828: Avoid multiple search of reserved regions during splitting

[Afshin Zafari]

To reserve two consequent memory regions, developers need to reserve a large region and then split it into two sub parts. To register memory type `(MEMFLAGS) mtXXX` for a region another call to NMT API is needed for every sub part. Since at every NMT call a linked list of reserved regions is searched, therefore for every split operation there are three NMT calls and search in the list.
This PR adds the memory flags of the two sub regions to the split API to avoid extra search in the list.

tiers1-5 tests passed

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Commit messages:
 - 8324828: Avoid multiple search of reserved regions during splitting

Changes: https://git.openjdk.org/jdk/pull/18001/files
 Webrev: https://webrevs.openjdk.org/?repo=jdk&pr=18001&range=00
  Issue: https://bugs.openjdk.org/browse/JDK-8324828
  Stats: 13 lines in 4 files changed: 3 ins; 3 del; 7 mod
  Patch: https://git.openjdk.org/jdk/pull/18001.diff
  Fetch: git fetch https://git.openjdk.org/jdk.git pull/18001/head:pull/18001

PR: https://git.openjdk.org/jdk/pull/18001