RFR: 8312585: Rename DisableTHPStackMitigation flag to THPStackMitigation [v2]

[Aleksey Shipilev]

> The flag newly added by [JDK-8312182](https://bugs.openjdk.org/browse/JDK-8312182) is prompting the use of `-XX:+DisableTHPStackMitigation` to disable the THP stack mitigation, thus allowing THP in thread stacks. This double negation does not read well, and not in line with other mitigation flags like `IntelJccErratumMitigation`.
> 
> It would be better to rename the flag to avoid double-negation, before it proliferates to other JDK releases.
> 
> (I would have the same comment during the original review, but missed it :P)
> 
> Additional testing: 
>  - [ ] GHA
>  - [x] Linux x86_64 fastdebug, affected test

Aleksey Shipilev 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 two additional commits since the last revision:

 - Merge branch 'master' into JDK-8312585-rename-thp-mitigation
 - Fix

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

Changes:
  - all: https://git.openjdk.org/jdk/pull/14992/files
  - new: https://git.openjdk.org/jdk/pull/14992/files/75b831e3..5756558e

Webrevs:
 - full: https://webrevs.openjdk.org/?repo=jdk&pr=14992&range=01
 - incr: https://webrevs.openjdk.org/?repo=jdk&pr=14992&range=00-01

  Stats: 14651 lines in 556 files changed: 8271 ins; 2736 del; 3644 mod
  Patch: https://git.openjdk.org/jdk/pull/14992.diff
  Fetch: git fetch https://git.openjdk.org/jdk.git pull/14992/head:pull/14992

PR: https://git.openjdk.org/jdk/pull/14992