RFR: 8244421: Wrong scrollbar position on touch enabled devices

[Jose Pereda]

`VirtualFlow` makes use of `VirtualScrollBar` controls, that are laid out next to the clipped container region, by
default.

However, when touch is supported, these scrollBars are floating controls laid out over the container. Therefore, in
this case, when the viewport dimensions are updated, the presence of the scrollBars shouldn't be taken into account.

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Commit messages:
 - Don’t resize viewport with scrollbar dimensions when touch is supported

Changes: https://git.openjdk.java.net/jfx/pull/208/files
 Webrev: https://webrevs.openjdk.java.net/jfx/208/webrev.00
  Issue: https://bugs.openjdk.java.net/browse/JDK-8244421
  Stats: 7 lines in 1 file changed: 5 ins; 0 del; 2 mod
  Patch: https://git.openjdk.java.net/jfx/pull/208.diff
  Fetch: git fetch https://git.openjdk.java.net/jfx pull/208/head:pull/208

PR: https://git.openjdk.java.net/jfx/pull/208