RFR: 8314149: Clipboard does inexact string comparison on mime type

[Ambarish Rapte]

The mime name should be exactly same as the mime type supported by platform.
Hence the comparison should not match partially similar names.
Added an invalid unit test.

@kevinrushforth @jayathirthrao please review

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Commit messages:
 - change wcsncmp to wcscmp

Changes: https://git.openjdk.org/jfx/pull/1207/files
 Webrev: https://webrevs.openjdk.org/?repo=jfx&pr=1207&range=00
  Issue: https://bugs.openjdk.org/browse/JDK-8314149
  Stats: 17 lines in 2 files changed: 11 ins; 3 del; 3 mod
  Patch: https://git.openjdk.org/jfx/pull/1207.diff
  Fetch: git fetch https://git.openjdk.org/jfx.git pull/1207/head:pull/1207

PR: https://git.openjdk.org/jfx/pull/1207