RFR: Updated ArrayCreation factories and bootstraps

[Dan Smith]

Added revised bootstrap and factories to ArrayCreation. Threaded through modifiers as much as possible. Added a branch in Array.newInstance to create null-checked arrays where currently supported by the VM.

Rewrote ArrayCreationTest to exercise all factories and bootstraps, and to make some use of modifiers.

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Commit messages:
 - fixes
 - Updated ArrayCreation factories and bootstraps

Changes: https://git.openjdk.org/valhalla/pull/1879/files
  Webrev: https://webrevs.openjdk.org/?repo=valhalla&pr=1879&range=00
  Stats: 1259 lines in 4 files changed: 1037 ins; 6 del; 216 mod
  Patch: https://git.openjdk.org/valhalla/pull/1879.diff
  Fetch: git fetch https://git.openjdk.org/valhalla.git pull/1879/head:pull/1879

PR: https://git.openjdk.org/valhalla/pull/1879