<Swing Dev> RFR: 8260719: Input method character moves with caret

[Denis Konoplev]

I've fixed annoying behaviour of input methods in text components. 
Code checks caret position before submitting composed text.

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Commit messages:
 - 8260719: Input method character moves with caret

Changes: https://git.openjdk.java.net/jdk/pull/2337/files
 Webrev: https://webrevs.openjdk.java.net/?repo=jdk&pr=2337&range=00
  Issue: https://bugs.openjdk.java.net/browse/JDK-8260719
  Stats: 16 lines in 1 file changed: 16 ins; 0 del; 0 mod
  Patch: https://git.openjdk.java.net/jdk/pull/2337.diff
  Fetch: git fetch https://git.openjdk.java.net/jdk pull/2337/head:pull/2337

PR: https://git.openjdk.java.net/jdk/pull/2337