RFR: 8323601: Improve LayoutPath.PathElement::toString

[Per Minborg]

This PR proposes to add an improved Improve `LayoutPath.PathElement::toString` method simplifying debugging.

Opinions and suggestions for `static PathElement sequenceElement(long start, long step)` are welcome.

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Commit messages:
 - Add toString to PathElement

Changes: https://git.openjdk.org/jdk/pull/17417/files
 Webrev: https://webrevs.openjdk.org/?repo=jdk&pr=17417&range=00
  Issue: https://bugs.openjdk.org/browse/JDK-8323601
  Stats: 62 lines in 3 files changed: 57 ins; 0 del; 5 mod
  Patch: https://git.openjdk.org/jdk/pull/17417.diff
  Fetch: git fetch https://git.openjdk.org/jdk.git pull/17417/head:pull/17417

PR: https://git.openjdk.org/jdk/pull/17417