[jfx11u] RFR: 8258381: [macos] Exception when input emoji using Chinese input method

[Johan Vos]

Clean backport.
This only touches the macos platform, build and basic tests work fine.

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Commit messages:
 - 8258381: [macos] Exception when input emoji using Chinese input method

Changes: https://git.openjdk.java.net/jfx11u/pull/15/files
 Webrev: https://webrevs.openjdk.java.net/?repo=jfx11u&pr=15&range=00
  Issue: https://bugs.openjdk.java.net/browse/JDK-8258381
  Stats: 2 lines in 1 file changed: 1 ins; 0 del; 1 mod
  Patch: https://git.openjdk.java.net/jfx11u/pull/15.diff
  Fetch: git fetch https://git.openjdk.java.net/jfx11u pull/15/head:pull/15

PR: https://git.openjdk.java.net/jfx11u/pull/15