[foreign-memaccess+abi] RFR: 8274287: Add a way to specify block size of unbounded arena allocator [v2]

[Maurizio Cimadamore]

> Following the discussion here:
> 
> https://mail.openjdk.java.net/pipermail/panama-dev/2021-May/013815.html
> 
> This patch renames arena allocator factories, to make room for new unbounded factory which allows clients to specify a custom block size.

Maurizio Cimadamore has updated the pull request incrementally with one additional commit since the last revision:

  Address review comments

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Changes:
  - all: https://git.openjdk.java.net/panama-foreign/pull/583/files
  - new: https://git.openjdk.java.net/panama-foreign/pull/583/files/eeea3f89..3ee0f9d9

Webrevs:
 - full: https://webrevs.openjdk.java.net/?repo=panama-foreign&pr=583&range=01
 - incr: https://webrevs.openjdk.java.net/?repo=panama-foreign&pr=583&range=00-01

  Stats: 13 lines in 2 files changed: 9 ins; 0 del; 4 mod
  Patch: https://git.openjdk.java.net/panama-foreign/pull/583.diff
  Fetch: git fetch https://git.openjdk.java.net/panama-foreign pull/583/head:pull/583

PR: https://git.openjdk.java.net/panama-foreign/pull/583