RFR: 8368478: RichTextArea: add IME support

[Andy Goryachev]

Adds Input Method Editor (IME) support to `RichTextArea`/`CodeArea`.

Tested on macOS and Windows 11 with Japanese and Chinese (pinyin) input methods.
Please test this on Linux, even though there is no platform-specific code in this PR (should work the same way it does in `TextArea`/`TextField`)

For testing, one can use the updated Monkey Tester
https://github.com/andy-goryachev-oracle/MonkeyTest
(optionally enable IME events in stdout with Logging -> IME Monitor)

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Commit messages:
 - test
 - accessor
 - cleanup
 - whitespace
 - Merge remote-tracking branch 'origin/master' into 8368478.ime
 - ime object
 - ime location
 - ime works
 - api

Changes: https://git.openjdk.org/jfx/pull/1938/files
  Webrev: https://webrevs.openjdk.org/?repo=jfx&pr=1938&range=00
  Issue: https://bugs.openjdk.org/browse/JDK-8368478
  Stats: 577 lines in 9 files changed: 496 ins; 56 del; 25 mod
  Patch: https://git.openjdk.org/jfx/pull/1938.diff
  Fetch: git fetch https://git.openjdk.org/jfx.git pull/1938/head:pull/1938

PR: https://git.openjdk.org/jfx/pull/1938