RFR: 8350567: NMT: update VMATree::register_mapping to copy the existing tag of the region [v5]

[Afshin Zafari]

> When committing a sub-region (SR) in the middle of a reserved region (RR), we need to decide on the MemTag. To find the correct tag, we had to find the RR base and take the tag and use it for SR.
> With this PR, there will be no need to find the RR base and the tag of the previous region of SR can be copied to the SR.
> 
> Tests:
> linux-x64-debug, gtest:NMT*, runtime/NMT

Afshin Zafari has updated the pull request with a new target base due to a merge or a rebase. The incremental webrev excludes the unrelated changes brought in by the merge/rebase. The pull request contains six additional commits since the last revision:

 - Merge remote-tracking branch 'origin/master' into _8350567_copy_tag_in_place
 - out tag of the begin node (stA) is used for accounting.
 - new test name, removed unnecessary code
 - removed extra whitespace.
 - unit test added.
 - 8350567: NMT: update VMATree::register_mapping to copy the existing tag of the region

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

Changes:
  - all: https://git.openjdk.org/jdk/pull/23771/files
  - new: https://git.openjdk.org/jdk/pull/23771/files/070a91c3..e2250990

Webrevs:
 - full: https://webrevs.openjdk.org/?repo=jdk&pr=23771&range=04
 - incr: https://webrevs.openjdk.org/?repo=jdk&pr=23771&range=03-04

  Stats: 25005 lines in 776 files changed: 9703 ins; 11967 del; 3335 mod
  Patch: https://git.openjdk.org/jdk/pull/23771.diff
  Fetch: git fetch https://git.openjdk.org/jdk.git pull/23771/head:pull/23771

PR: https://git.openjdk.org/jdk/pull/23771