RFR: 8313202: MutexLocker should disallow null Mutexes [v7]

[Aleksey Shipilev]

> As seen in [JDK-8313081](https://bugs.openjdk.org/browse/JDK-8313081), it is fairly easy to pass nullptr `Mutex` to `MutexLocker` by accident, which would just silently avoid the lock.
> 
> There are a few places in Hotspot where we pass `nullptr` to simulate re-entrancy and/or conditionally take the lock. Those places can be more explicit, and the default `MutexLocker` can disallow nullptrs for extra safety.
> 
> More thorough testing with different GC/JIT combinations is running now, we might find more issues there. Meanwhile, please comment on the approach.
> 
> Additional testing:
>  - [x] `grep -R "MutexLocker " src/hotspot | grep -i null`, only new `ConditionalMutexLocker` hits
>  - [x] `grep -R "MutexLocker " src/hotspot | grep -i ?`, no hits
>  - [x] Linux AArch64 fastdebug, `tier1 tier2 tier3` x `Serial Parallel G1 Shenandoah`

Aleksey Shipilev has updated the pull request incrementally with three additional commits since the last revision:

 - Touchup whitespace
 - Rewrite jvmtiManageCapabilities lock usage
 - Re-instate old asserts

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

Changes:
  - all: https://git.openjdk.org/jdk/pull/15043/files
  - new: https://git.openjdk.org/jdk/pull/15043/files/8dc9cde7..3676fa71

Webrevs:
 - full: https://webrevs.openjdk.org/?repo=jdk&pr=15043&range=06
 - incr: https://webrevs.openjdk.org/?repo=jdk&pr=15043&range=05-06

  Stats: 35 lines in 3 files changed: 15 ins; 8 del; 12 mod
  Patch: https://git.openjdk.org/jdk/pull/15043.diff
  Fetch: git fetch https://git.openjdk.org/jdk.git pull/15043/head:pull/15043

PR: https://git.openjdk.org/jdk/pull/15043