RFR: 8271091: Missing API docs in UI controls classes

[Ajit Ghaisas]

This PR fixes javadoc warnings in javafx.controls and javafx.web modules.
Note : 
- The javadoc needs to be generated with the JDK 18 EA build.
- There are still 20 javadoc warnings remaining in javafx.controls module and 3 warnings remaining in javafx.web module. The root cause is different and they will be addressed under [JDK-8270996](https://bugs.openjdk.java.net/browse/JDK-8270996)

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Commit messages:
 - 8271091 - fix javadoc warnings

Changes: https://git.openjdk.java.net/jfx/pull/646/files
 Webrev: https://webrevs.openjdk.java.net/?repo=jfx&pr=646&range=00
  Issue: https://bugs.openjdk.java.net/browse/JDK-8271091
  Stats: 248 lines in 49 files changed: 114 ins; 11 del; 123 mod
  Patch: https://git.openjdk.java.net/jfx/pull/646.diff
  Fetch: git fetch https://git.openjdk.java.net/jfx pull/646/head:pull/646

PR: https://git.openjdk.java.net/jfx/pull/646