RFR: 8281384: Random chars on paste from Windows clipboard

[Oliver Schmidtmer]

Windows programs may reuse a clipboard buffer that is larger than the new content. In this case de NUL terminator is not at the end of the buffer, but within it. 
The current implementation copys the whole buffer into a text field, including the NUL terminator and the remaining chars.

The JIRA ticket contains a JNA based sample program, which prefills the buffer for demonstrating this issue.
If this should be added as a unit test, I'm open for advice how to do that.

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Commit messages:
 - JDK-8281384: Random chars on paste from Windows clipboard

Changes: https://git.openjdk.org/jfx/pull/1724/files
  Webrev: https://webrevs.openjdk.org/?repo=jfx&pr=1724&range=00
  Issue: https://bugs.openjdk.org/browse/JDK-8281384
  Stats: 9 lines in 1 file changed: 8 ins; 0 del; 1 mod
  Patch: https://git.openjdk.org/jfx/pull/1724.diff
  Fetch: git fetch https://git.openjdk.org/jfx.git pull/1724/head:pull/1724

PR: https://git.openjdk.org/jfx/pull/1724