RFR: Add NULL_CHECKED flag to array creation calls

[Maurizio Cimadamore]

The synthetic calls to `ArrayCreation` for non-null array initializers should pass the `NULL_CHECKED` flag, so that the library can act accordingly.

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Commit messages:
 - Add NULL_CHECK flag to array creation calls

Changes: https://git.openjdk.org/valhalla/pull/1898/files
  Webrev: https://webrevs.openjdk.org/?repo=valhalla&pr=1898&range=00
  Stats: 4 lines in 1 file changed: 0 ins; 3 del; 1 mod
  Patch: https://git.openjdk.org/valhalla/pull/1898.diff
  Fetch: git fetch https://git.openjdk.org/valhalla.git pull/1898/head:pull/1898

PR: https://git.openjdk.org/valhalla/pull/1898