RFR: 8378389: Remove AppContext from the Swing RepaintManager

[Phil Race]

Remove AppContext from RepaintManager

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Commit messages:
 - 8378389

Changes: https://git.openjdk.org/jdk/pull/29862/files
  Webrev: https://webrevs.openjdk.org/?repo=jdk&pr=29862&range=00
  Issue: https://bugs.openjdk.org/browse/JDK-8378389
  Stats: 52 lines in 4 files changed: 4 ins; 19 del; 29 mod
  Patch: https://git.openjdk.org/jdk/pull/29862.diff
  Fetch: git fetch https://git.openjdk.org/jdk.git pull/29862/head:pull/29862

PR: https://git.openjdk.org/jdk/pull/29862