RFR: 8278134: Move static utility methods to infrastructure (EditAndScrollTest)

[Jeanette Winzenburg]

Extracted static test utility methods from EditAndScrollTest into new VirtualizedControlTestUtils, added rudimentary tests for the methods.

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Commit messages:
- 8278134: Move static utility methods to infrastructure

Changes: https://git.openjdk.java.net/jfx/pull/690/files
Webrev: https://webrevs.openjdk.java.net/?repo=jfx&pr=690&range=00
Issue: https://bugs.openjdk.java.net/browse/JDK-8278134
Stats: 348 lines in 3 files changed: 290 ins; 57 del; 1 mod
Patch: https://git.openjdk.java.net/jfx/pull/690.diff
Fetch: git fetch https://git.openjdk.java.net/jfx pull/690/head:pull/690

PR: https://git.openjdk.java.net/jfx/pull/690