[jfx17] RFR: 8250590: Classes and methods in the javafx.css package are missing documentation

[Ajit Ghaisas]

This PR corrects/adds missing documentation for classes in javafx.css package.

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Commit messages:
 - 8250590 - CSS Javadoc corrections

Changes: https://git.openjdk.java.net/jfx/pull/589/files
 Webrev: https://webrevs.openjdk.java.net/?repo=jfx&pr=589&range=00
  Issue: https://bugs.openjdk.java.net/browse/JDK-8250590
  Stats: 494 lines in 29 files changed: 443 ins; 4 del; 47 mod
  Patch: https://git.openjdk.java.net/jfx/pull/589.diff
  Fetch: git fetch https://git.openjdk.java.net/jfx pull/589/head:pull/589

PR: https://git.openjdk.java.net/jfx/pull/589