[lworld] RFR: 8377162: [lworld] getResourceAsStream() doesn't work in preview mode for exploded images

[David Beaumont]

Allow exploded module readers created for exploded system images to support preview mode.

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Commit messages:
 - Preview mode for exploded system module readers

Changes: https://git.openjdk.org/valhalla/pull/2032/files
  Webrev: https://webrevs.openjdk.org/?repo=valhalla&pr=2032&range=00
  Issue: https://bugs.openjdk.org/browse/JDK-8377162
  Stats: 150 lines in 4 files changed: 135 ins; 1 del; 14 mod
  Patch: https://git.openjdk.org/valhalla/pull/2032.diff
  Fetch: git fetch https://git.openjdk.org/valhalla.git pull/2032/head:pull/2032

PR: https://git.openjdk.org/valhalla/pull/2032