RFR: 8261840: Submenus close to screen borders are no longer repositioned

[Robert Lichtenberger]

Reverting to the old way of showing the context menu but with application
of CSS prior to calling prefHeight(-1) / prefWidth(-1) to ensure correct
size measurement of the menu.

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Commit messages:
 - 8261840: Submenus close to screen borders are no longer repositioned

Changes: https://git.openjdk.java.net/jfx/pull/410/files
 Webrev: https://webrevs.openjdk.java.net/?repo=jfx&pr=410&range=00
  Issue: https://bugs.openjdk.java.net/browse/JDK-8261840
  Stats: 58 lines in 1 file changed: 5 ins; 40 del; 13 mod
  Patch: https://git.openjdk.java.net/jfx/pull/410.diff
  Fetch: git fetch https://git.openjdk.java.net/jfx pull/410/head:pull/410

PR: https://git.openjdk.java.net/jfx/pull/410