RFR: 8199592: Control labels truncated at certain DPI scaling levels

[Jose Pereda]

As commented in the [JBS issue](https://bugs.openjdk.java.net/browse/JDK-8199592), the default UI scale 1.0 is used to perform initial calculations of preferred sizes of the scene, even if the scale has already a different value (i.e 175%). As a workaround, calling `Stage::sizeToScene` fix it, as it forces to do new calculations but now with the correct UI scale.

This PR moves the call to `Window::updateOutputScales` before the scene initialization takes place, so the UI scale is correctly set for the initial preferred size of the scene, and no workaround is required.

It also provides a system test that can be tested on Linux and Windows. Before applying the fix, the `Check` text of the checkboxes is rendered as `Che...`. With the fix, the test verifies, for a given UI scale, that the rendered text is `Check`.

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Commit messages:
 - Call updateOutputScales before the scene initialization, including system test

Changes: https://git.openjdk.java.net/jfx/pull/351/files
 Webrev: https://webrevs.openjdk.java.net/?repo=jfx&pr=351&range=00
  Issue: https://bugs.openjdk.java.net/browse/JDK-8199592
  Stats: 121 lines in 2 files changed: 115 ins; 6 del; 0 mod
  Patch: https://git.openjdk.java.net/jfx/pull/351.diff
  Fetch: git fetch https://git.openjdk.java.net/jfx pull/351/head:pull/351

PR: https://git.openjdk.java.net/jfx/pull/351