RFR: 8356634: VectorShape#largestShapeFor should have public access

[Ian Graves]

VectorShape#largestShapeFor is referenced in existing JavaDoc but has been package-private. This propose change makes it public and adds documentation for it.

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Commit messages:
 - Making VectorShape.largestShapeFor public and documenting

Changes: https://git.openjdk.org/jdk/pull/25513/files
  Webrev: https://webrevs.openjdk.org/?repo=jdk&pr=25513&range=00
  Issue: https://bugs.openjdk.org/browse/JDK-8356634
  Stats: 12 lines in 1 file changed: 8 ins; 0 del; 4 mod
  Patch: https://git.openjdk.org/jdk/pull/25513.diff
  Fetch: git fetch https://git.openjdk.org/jdk.git pull/25513/head:pull/25513

PR: https://git.openjdk.org/jdk/pull/25513