RFR: 8375350: Remove usage of AppContext from javax.imageio implementation

[Phil Race]

Remove usage of AppContext from Image IO

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Commit messages:
 - 8375350

Changes: https://git.openjdk.org/jdk/pull/29236/files
  Webrev: https://webrevs.openjdk.org/?repo=jdk&pr=29236&range=00
  Issue: https://bugs.openjdk.org/browse/JDK-8375350
  Stats: 14 lines in 1 file changed: 2 ins; 10 del; 2 mod
  Patch: https://git.openjdk.org/jdk/pull/29236.diff
  Fetch: git fetch https://git.openjdk.org/jdk.git pull/29236/head:pull/29236

PR: https://git.openjdk.org/jdk/pull/29236