[jfx22] RFR: 8314147: Updated the PhongMaterial documentation

[Nir Lisker]

This pull request contains a backport of commit [d9645730](https://github.com/openjdk/jfx/commit/d9645730f1e76e95e0bb93ceaeb5550390bf95c1) from the [openjdk/jfx](https://git.openjdk.org/jfx) repository.

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Commit messages:
 - Backport d9645730f1e76e95e0bb93ceaeb5550390bf95c1

Changes: https://git.openjdk.org/jfx/pull/1385/files
 Webrev: https://webrevs.openjdk.org/?repo=jfx&pr=1385&range=00
  Issue: https://bugs.openjdk.org/browse/JDK-8314147
  Stats: 521 lines in 39 files changed: 461 ins; 13 del; 47 mod
  Patch: https://git.openjdk.org/jfx/pull/1385.diff
  Fetch: git fetch https://git.openjdk.org/jfx.git pull/1385/head:pull/1385

PR: https://git.openjdk.org/jfx/pull/1385