[lworld] RFR: 8373987: [lworld] exploded-image/test broken since disable patching (JDK-8373806)

[David Beaumont]

Hopefully a fix for preview mode with exploded images in classLoader.cpp.

I did a little renaming since now it's clear that "preview mode" isn't a thing that's limited only to a jimage being present.

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Commit messages:
 - Seems to work ...

Changes: https://git.openjdk.org/valhalla/pull/1845/files
  Webrev: https://webrevs.openjdk.org/?repo=valhalla&pr=1845&range=00
  Issue: https://bugs.openjdk.org/browse/JDK-8373987
  Stats: 61 lines in 3 files changed: 28 ins; 9 del; 24 mod
  Patch: https://git.openjdk.org/valhalla/pull/1845.diff
  Fetch: git fetch https://git.openjdk.org/valhalla.git pull/1845/head:pull/1845

PR: https://git.openjdk.org/valhalla/pull/1845