RFR: 8276313: ScrollPane scroll delta incorrectly depends on content height [v3]

[Michael Strauß]

> This PR fixes an issue where the scroll delta of ScrollPane incorrectly depends on the size of its content.
> This leads to extremely slow scrolling when the content is only slightly larger than the ScrollPane.

Michael Strauß has updated the pull request incrementally with one additional commit since the last revision:

  Changes per review

-------------

Changes:
  - all: https://git.openjdk.java.net/jfx/pull/660/files
  - new: https://git.openjdk.java.net/jfx/pull/660/files/147858d7..6b8985f7

Webrevs:
 - full: https://webrevs.openjdk.java.net/?repo=jfx&pr=660&range=02
 - incr: https://webrevs.openjdk.java.net/?repo=jfx&pr=660&range=01-02

  Stats: 12 lines in 1 file changed: 0 ins; 0 del; 12 mod
  Patch: https://git.openjdk.java.net/jfx/pull/660.diff
  Fetch: git fetch https://git.openjdk.java.net/jfx pull/660/head:pull/660

PR: https://git.openjdk.java.net/jfx/pull/660