[lworld] RFR: 8367551: Cherrypick ImageReader refactoring PR (JDK-8360037)

[David Beaumont]

Cherry pick ImageReader work to unblock progress on preview mode in Valhalla.

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Commit messages:
 - Cherrypick ImageReader refactoring (JDK-8360037)

Changes: https://git.openjdk.org/valhalla/pull/1581/files
  Webrev: https://webrevs.openjdk.org/?repo=valhalla&pr=1581&range=00
  Issue: https://bugs.openjdk.org/browse/JDK-8367551
  Stats: 2319 lines in 10 files changed: 1702 ins; 369 del; 248 mod
  Patch: https://git.openjdk.org/valhalla/pull/1581.diff
  Fetch: git fetch https://git.openjdk.org/valhalla.git pull/1581/head:pull/1581

PR: https://git.openjdk.org/valhalla/pull/1581