RFR: 8245183: Two fxml unit tests log warnings about deprecated escape sequences

[Ajit Ghaisas]

Issue : https://bugs.openjdk.java.net/browse/JDK-8245183
Fix : Added a message to the test saying these are expected warnings. Refer JBS comments for more details.

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Commit messages:
 - Add expected warning message

Changes: https://git.openjdk.java.net/jfx/pull/225/files
 Webrev: https://webrevs.openjdk.java.net/jfx/225/webrev.00
  Issue: https://bugs.openjdk.java.net/browse/JDK-8245183
  Stats: 5 lines in 2 files changed: 3 ins; 0 del; 2 mod
  Patch: https://git.openjdk.java.net/jfx/pull/225.diff
  Fetch: git fetch https://git.openjdk.java.net/jfx pull/225/head:pull/225

PR: https://git.openjdk.java.net/jfx/pull/225