RFR: 8365165: Zap C-heap memory at delete/free

[Aleksey Shipilev]

We sometimes have a lifecycle problem with C-heap allocated objects. The most recent I dealt with is [JDK-8364501](https://bugs.openjdk.org/browse/JDK-8364501). It would be convenient to have diagnostic code to zap the memory that is freed on C heap. We already do this for alloc/realloc. When NMT is enabled (which it is for debug builds), we can also do this for frees, as NMT tells us the size of the free-ed block.

This PR introduces a new diagnostic flag to match other `Zap*` flags we already have, puts the zapping on free path, and wraps alloc/realloc zapping with the flag as well. The last part is not really necessary, but it is nicer to wrap zapping code with a flag like this, so we can disable it for testing performance. JCStress routinely opts-out of most of the zapping to gain higher sampling throughput on fastdebug builds.

Additional testing:
 - [x] Linux AArch64 server fastdebug, selectively rolling back [JDK-8364501](https://bugs.openjdk.org/browse/JDK-8364501) -- starts to immediately crash on reproducer
 - [ ] Linux AArch64 server fastdebug, `all` (no new crashes)
 - [ ] Linux x86_64 server fastdebug, `all` (no new crashes)

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

Commit messages:
 - More flag uses
 - Fix

Changes: https://git.openjdk.org/jdk/pull/26775/files
  Webrev: https://webrevs.openjdk.org/?repo=jdk&pr=26775&range=00
  Issue: https://bugs.openjdk.org/browse/JDK-8365165
  Stats: 12 lines in 3 files changed: 9 ins; 0 del; 3 mod
  Patch: https://git.openjdk.org/jdk/pull/26775.diff
  Fetch: git fetch https://git.openjdk.org/jdk.git pull/26775/head:pull/26775

PR: https://git.openjdk.org/jdk/pull/26775