RFR: 8367045: [Linux] Dead keys not working

[Thiago Milczarek Sayao]

The bug report is on Linux Mint which does not use ibus (the gnome default).

With this change, it continues to work on ibus, but also works works without it (on mint).

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Commit messages:
 - 8367045
 - 8367045
 - 8367045
 - 8367045
 - 8367045
 - 8367045
 - 8367045
 - 8367045
 - IME

Changes: https://git.openjdk.org/jfx/pull/1922/files
  Webrev: https://webrevs.openjdk.org/?repo=jfx&pr=1922&range=00
  Issue: https://bugs.openjdk.org/browse/JDK-8367045
  Stats: 25 lines in 2 files changed: 5 ins; 5 del; 15 mod
  Patch: https://git.openjdk.org/jfx/pull/1922.diff
  Fetch: git fetch https://git.openjdk.org/jfx.git pull/1922/head:pull/1922

PR: https://git.openjdk.org/jfx/pull/1922