[lworld] RFR: 8372038: [lworld] Update ExplodedImage to use preview mode correctly [v2]

[David Beaumont]

> Adds preview mode support for ExplodedImage.
> 
> Adds tests so both ExplodedImage and ImageReader implementations of SystemImage are tested with exactly the same test data and assertions.

David Beaumont has updated the pull request incrementally with one additional commit since the last revision:

  fixing duplicate elements

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

Changes:
  - all: https://git.openjdk.org/valhalla/pull/1743/files
  - new: https://git.openjdk.org/valhalla/pull/1743/files/f7d8efd4..9abfa314

Webrevs:
 - full: https://webrevs.openjdk.org/?repo=valhalla&pr=1743&range=01
 - incr: https://webrevs.openjdk.org/?repo=valhalla&pr=1743&range=00-01

  Stats: 40 lines in 2 files changed: 17 ins; 0 del; 23 mod
  Patch: https://git.openjdk.org/valhalla/pull/1743.diff
  Fetch: git fetch https://git.openjdk.org/valhalla.git pull/1743/head:pull/1743

PR: https://git.openjdk.org/valhalla/pull/1743