RFR: 8297718: Make NMT free:ing protocol more granular [v3]

[Johan Sjölen]

> This PR avoids the double registration of a failed `os::realloc` in NMT by doing the NMT free protocol steps inline (asserting block integrity, marking of MallocHeader, and registrering results to statistics). This is done by creating a new struct `FreePackage` which includes all of the necessary data for registrering results.
> 
> I also did some light refactoring which I think makes the protocol clearer, these are done piece wise as separate commits for the reviewers' convenience.

Johan Sjölen has updated the pull request incrementally with one additional commit since the last revision:

  Nits

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Changes:
  - all: https://git.openjdk.org/jdk/pull/11390/files
  - new: https://git.openjdk.org/jdk/pull/11390/files/e704c024..bf560998

Webrevs:
 - full: https://webrevs.openjdk.org/?repo=jdk&pr=11390&range=02
 - incr: https://webrevs.openjdk.org/?repo=jdk&pr=11390&range=01-02

  Stats: 2 lines in 2 files changed: 0 ins; 0 del; 2 mod
  Patch: https://git.openjdk.org/jdk/pull/11390.diff
  Fetch: git fetch https://git.openjdk.org/jdk pull/11390/head:pull/11390

PR: https://git.openjdk.org/jdk/pull/11390