RFR: 8270996: javadoc: missing comments in serialized classes

[Andy Goryachev]

Adding `@SuppressWarnings("doclint")` to Serializable classes to silence the javadoc "missing comments" warning.
(There is no javadoc command group for serialization like doclint:missing) 

Pros:
- the classes are fairly stable, we can ask the reviewers to pay extra attention to any javadoc changes

Cons: 
- all javadoc warnings will be suppressed

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Commit messages:
 - 8270996: JavaFX serialized classes get javadoc warnings for missing comments

Changes: https://git.openjdk.org/jfx/pull/1386/files
 Webrev: https://webrevs.openjdk.org/?repo=jfx&pr=1386&range=00
  Issue: https://bugs.openjdk.org/browse/JDK-8270996
  Stats: 54 lines in 25 files changed: 33 ins; 0 del; 21 mod
  Patch: https://git.openjdk.org/jfx/pull/1386.diff
  Fetch: git fetch https://git.openjdk.org/jfx.git pull/1386/head:pull/1386

PR: https://git.openjdk.org/jfx/pull/1386