<AWT Dev> RFR: 8258805: Japanese characters not entered by mouse click on Windows 10

[Dmitry Markov]

Problem description:
The IME behaviour has changed starting from recent Windows 10 builds. In particular if the complex characters (Japanese, Chinese, etc.) are entered to some component and the focus is transferred to another component (which does not support the IM) the IM is disabled and the unconfirmed composition string gets discarded.
On previous Windows versions in the same situation the composition string is not discarded.

Fix:
It is necessary to take care of unconfirmed composition string once the IME is going to be disabled.

Testing:
All our automated regression and JCK tests passed with the proposed change.

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Commit messages:
 - 8258805: Japanese characters not entered by mouse click on Windows 10

Changes: https://git.openjdk.java.net/jdk/pull/2142/files
 Webrev: https://webrevs.openjdk.java.net/?repo=jdk&pr=2142&range=00
  Issue: https://bugs.openjdk.java.net/browse/JDK-8258805
  Stats: 6 lines in 1 file changed: 5 ins; 0 del; 1 mod
  Patch: https://git.openjdk.java.net/jdk/pull/2142.diff
  Fetch: git fetch https://git.openjdk.java.net/jdk pull/2142/head:pull/2142

PR: https://git.openjdk.java.net/jdk/pull/2142