RFR: 8282100: Missed top/left bouncing for ScrollPane on Raspberry Pi with Touchscreen

[Alexander Scherbatiy]

There is the bouncing when scrolling a node on a ScrollPane to the right/bottom (the node on the scroll pane is scrolled further than its width/height so the background is visible and then automatically is scrolled back to the node bounds) on Raspberry Pi with Touchscreen.
There is no bouncing when node is scrolled to the left/top.

The fix updates ScrollPaneSkin.updatePosX()/updatePosY() methods to not discard negative minX/Y values in case the touch is supported.

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Commit messages:
 - 8282100: Missed top/left bouncing for ScrollPane on Raspberry Pi with Touchscreen

Changes: https://git.openjdk.java.net/jfx/pull/736/files
 Webrev: https://webrevs.openjdk.java.net/?repo=jfx&pr=736&range=00
  Issue: https://bugs.openjdk.java.net/browse/JDK-8282100
  Stats: 8 lines in 1 file changed: 6 ins; 0 del; 2 mod
  Patch: https://git.openjdk.java.net/jfx/pull/736.diff
  Fetch: git fetch https://git.openjdk.java.net/jfx pull/736/head:pull/736

PR: https://git.openjdk.java.net/jfx/pull/736