[lworld] RFR: 8354529: [lworld] Add tests for flat arrays in CDS archive [v2]

[Matias Saavedra Silva]

> With CDS and AOT now fully supported in lworld, we need better test coverage to ensure that flat arrays are archived correctly. This patch adds a test to check that an array of both a migrate value class and a flattenable user defined value class can be archived and restored correctly in a static CDS dump. 
> 
> During the process it was discovered that the object subgraph was overlooking the element class of flat arrays, so proper handling was added courtesy of @iklam.
> 
> Verified with tier 1-5 tests.

Matias Saavedra Silva has updated the pull request incrementally with one additional commit since the last revision:

  ioi comment and additional testing

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Changes:
  - all: https://git.openjdk.org/valhalla/pull/2081/files
  - new: https://git.openjdk.org/valhalla/pull/2081/files/45996133..4138e452

Webrevs:
 - full: https://webrevs.openjdk.org/?repo=valhalla&pr=2081&range=01
 - incr: https://webrevs.openjdk.org/?repo=valhalla&pr=2081&range=00-01

  Stats: 94 lines in 2 files changed: 47 ins; 23 del; 24 mod
  Patch: https://git.openjdk.org/valhalla/pull/2081.diff
  Fetch: git fetch https://git.openjdk.org/valhalla.git pull/2081/head:pull/2081

PR: https://git.openjdk.org/valhalla/pull/2081