RFR: 8311648: Refactor the Arena/Chunk/ChunkPool interface [v8]

[Johan Sjölen]

> Hi,
> 
> This PR refactors the Arena code without introducing any changes in behavior. I believe that this leads to a much clearer API and that this will in turn simplify the maintenance of this code. `Chunk` is now much more "dumb", mainly acting as a way of interrogating the chunk of data that it is holding. The `ChunkPool` gains a more prominent role, being entirely responsible for the memory allocation strategy used. `Arena` is basically unchanged, as it orchestrates the usage of these two APIs. The `chop` and `next_chop` methods are re-defined to be static inside of `Chunk`, having an object `delete` itself  is very surprising, so I'm happy to get rid of that.
> 
> I hope that you agree with me on these changes!
> 
> Cheers,
> Johan

Johan Sjölen has updated the pull request incrementally with two additional commits since the last revision:

 - Mention that it's null-terminated
 - Comments etc

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

Changes:
  - all: https://git.openjdk.org/jdk/pull/14803/files
  - new: https://git.openjdk.org/jdk/pull/14803/files/c688bb55..642166c2

Webrevs:
 - full: https://webrevs.openjdk.org/?repo=jdk&pr=14803&range=07
 - incr: https://webrevs.openjdk.org/?repo=jdk&pr=14803&range=06-07

  Stats: 3 lines in 1 file changed: 2 ins; 0 del; 1 mod
  Patch: https://git.openjdk.org/jdk/pull/14803.diff
  Fetch: git fetch https://git.openjdk.org/jdk.git pull/14803/head:pull/14803

PR: https://git.openjdk.org/jdk/pull/14803