[lworld] RFR: 8378365: [lworld] Replace use of regular expression in ExplodedImage

[David Beaumont]

Fixes regex related issue before migration of ExplodedImage changes into mainline.

Test already present for "bad" paths in:
test/jdk/jdk/internal/jrtfs/SystemImageTest.java
but I will add a few more.

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Commit messages:
 - fix off-by-one error in path test
 - Add negative test data with '.' and '..' in
 - Swap out regex for non-revursive path check

Changes: https://git.openjdk.org/valhalla/pull/2147/files
  Webrev: https://webrevs.openjdk.org/?repo=valhalla&pr=2147&range=00
  Issue: https://bugs.openjdk.org/browse/JDK-8378365
  Stats: 47 lines in 2 files changed: 34 ins; 4 del; 9 mod
  Patch: https://git.openjdk.org/valhalla/pull/2147.diff
  Fetch: git fetch https://git.openjdk.org/valhalla.git pull/2147/head:pull/2147

PR: https://git.openjdk.org/valhalla/pull/2147