RFR: 8260013: Snapshot does not work for nodes in a subscene

[Lukasz Kostyra]

Originally this issue showed the problem of Node being incorrectly rendered (clipped) when snapshotting, compared to a snapshot of the whole Scene. Later on there was another problem added - lights not being taken into account if they are added to a SubScene.

As it later turned out, the original problem from this bug report is a problem with ParallelCamera incorrectly estimating near/far clipping planes, which just happened to reveal itself while snapshotting a Node. During testing I found out you can make the Node clip regardless of snapshot mechanism. Clipping issue was moved to a separate bug report and this PR only fixes the inconsistency in lights being gathered for a snapshot.

`Scene.doSnapshot()` was expanded to also check if SubScene provided to it is non-null and to fetch lights assigned to it. Scenario was tested with added SnapshotLightsTest.

Rest of the tests were checked and don't produce any noticeable regressions.

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Commit messages:
 - Move test out of robot tests, update copyrights
 - Add test for snapshot lights inconsistency
 - Include subscene lights in snapshot

Changes: https://git.openjdk.org/jfx/pull/1332/files
 Webrev: https://webrevs.openjdk.org/?repo=jfx&pr=1332&range=00
  Issue: https://bugs.openjdk.org/browse/JDK-8260013
  Stats: 184 lines in 4 files changed: 173 ins; 0 del; 11 mod
  Patch: https://git.openjdk.org/jfx/pull/1332.diff
  Fetch: git fetch https://git.openjdk.org/jfx.git pull/1332/head:pull/1332

PR: https://git.openjdk.org/jfx/pull/1332