RFR: 8299915: Remove ArrayAllocatorMallocLimit and associated code [v6]

[Justin King]

> Remove abstraction that is a holdover from Solaris. Direct usages of `MmapArrayAllocator` have been switched to normal `malloc`. The justification is that none of the code paths are called from signal handlers, so using `mmap` directly does not make sense and is potentially slower than going through `malloc` which can potentially re-use memory without making any system calls. The remaining usages of `ArrayAllocator` and `MallocArrayAllocator` are equivalent.

Justin King has updated the pull request incrementally with one additional commit since the last revision:

  Ensure Padded2DArray clears memory to preserve compatibility with mmap
  
  Signed-off-by: Justin King <jcking at google.com>

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Changes:
  - all: https://git.openjdk.org/jdk/pull/11931/files
  - new: https://git.openjdk.org/jdk/pull/11931/files/d30748e9..cf3097ec

Webrevs:
 - full: https://webrevs.openjdk.org/?repo=jdk&pr=11931&range=05
 - incr: https://webrevs.openjdk.org/?repo=jdk&pr=11931&range=04-05

  Stats: 4 lines in 1 file changed: 3 ins; 0 del; 1 mod
  Patch: https://git.openjdk.org/jdk/pull/11931.diff
  Fetch: git fetch https://git.openjdk.org/jdk pull/11931/head:pull/11931

PR: https://git.openjdk.org/jdk/pull/11931