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