RFR: 8339735: Remove references to Applet in core-libs/security APIs

[Justin Lu]

Please review this PR which removes occurrences of 'applet' within the corelibs specification. Applet has been deprecated since JDK9, and may be a confusing term for new Java developers, so it should be removed from the documentation.

Primarily, usages where 'applet' is used interchangeably with 'application' are removed.
This change does not include removal of usages in a historical sense. For example, something such as 


 * @apiNote
 * Thread groups provided a way in early Java releases to group threads and provide
 * a form of <i>job control</i> for threads. Thread groups supported the isolation
 * of applets and defined methods intended for diagnostic purposes. It should be
 * rare for new applications to create ThreadGroups and interact with this API.


in _src/java.base/share/classes/java/lang/ThreadGroup.java_. 
Please see the JBS issue comments for further reasoning on why other occurrences were not removed.

-------------

Commit messages:
 - init

Changes: https://git.openjdk.org/jdk/pull/21046/files
  Webrev: https://webrevs.openjdk.org/?repo=jdk&pr=21046&range=00
  Issue: https://bugs.openjdk.org/browse/JDK-8339735
  Stats: 17 lines in 7 files changed: 0 ins; 1 del; 16 mod
  Patch: https://git.openjdk.org/jdk/pull/21046.diff
  Fetch: git fetch https://git.openjdk.org/jdk.git pull/21046/head:pull/21046

PR: https://git.openjdk.org/jdk/pull/21046