RFR: 8359053: Implement JEP 504 - Remove the Applet API

[Phil Race]

This is the implementation of JEP 504 - Remove the Applet API.
API changes are
- Remove the entire java.applet package
- Remove the javax/swing/JApplet class
- Remove applet related APIs in java.beans
- Update javadoc referring to applets, including one gif image - now changed to an svg image
- 
Other changes are
- Remove references to the removed classes
- Remove obsolete tests
- Update obsolete code comments

sun.awt.AppContext is even more obsolete now than it was before, but eliminating uses of that will be is not required,
and will be follow-on internal clean up, at a later date, under unrelated bug ids, and likely not completed in the same
release as this JEP is integrated.

I have extensively tested this - running all the automated tests used by CI tiers 1 to 8.

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Commit messages:
 - 8359053

Changes: https://git.openjdk.org/jdk/pull/25698/files
  Webrev: https://webrevs.openjdk.org/?repo=jdk&pr=25698&range=00
  Issue: https://bugs.openjdk.org/browse/JDK-8359053
  Stats: 3120 lines in 74 files changed: 114 ins; 2867 del; 139 mod
  Patch: https://git.openjdk.org/jdk/pull/25698.diff
  Fetch: git fetch https://git.openjdk.org/jdk.git pull/25698/head:pull/25698

PR: https://git.openjdk.org/jdk/pull/25698