[jfx22] RFR: 8221261: Deadlock on macOS in JFXPanel app when handling IME calls

[Kevin Rushforth]

Clean backport of a safe fix for this critical deadlock bug to the jfx22 stabilization branch during RDP1.

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Commit messages:
 - Backport 90cbc66305d0a1380cf3a8cd99ad40db240e554c

Changes: https://git.openjdk.org/jfx/pull/1334/files
 Webrev: https://webrevs.openjdk.org/?repo=jfx&pr=1334&range=00
  Issue: https://bugs.openjdk.org/browse/JDK-8221261
  Stats: 30 lines in 1 file changed: 28 ins; 0 del; 2 mod
  Patch: https://git.openjdk.org/jfx/pull/1334.diff
  Fetch: git fetch https://git.openjdk.org/jfx.git pull/1334/head:pull/1334

PR: https://git.openjdk.org/jfx/pull/1334