RFR: 8322619: Parts of SG no longer update during rendering - overlapping - culling - dirty

[eduardsdv]

This is an alternative solution to the PR: https://github.com/openjdk/jfx/pull/1310.

This solution is based on the invariant that if a node is marked as dirty, all ancestors must also be marked as dirty and that if an ancestor is marked as clean, all descendants must also be marked as clean. 
Therefore I removed the ``clearDirtyTree()`` method and put its content to the ``clearDirty()`` method.

Furthermore, since dirty flag is only used when rendering by ``ViewPainter``, it should also be deleted by ``ViewPainter`` only. 
This guarantees:
1. that all dirty flags are removed after rendering, and 
2. that no dirty flags are removed when a node is rendered, e.g. by creating a snapshot or printing.
Therefore I removed all calls of the methods ``clearDirty()`` and ``clearDirtyTree()`` from all other classes except the ``ViewerPainter``.

The new version of the ``clearDirty()`` method together with calling it from the ``ViewerPainter`` needs to visit far fewer nodes compared to the version prior this PR.

The supplied test checks that the nodes are updated even if they are partially covered, which led to the error in the version before the PR. The test can be started with ``gradlew -PFULL_TEST=true :systemTests:test --tests NGNodeDirtyFlagTest``

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Commit messages:
 - JDK-8322619: Combine clearDirtyTree() and clearDirty() methods.

Changes: https://git.openjdk.org/jfx/pull/1451/files
  Webrev: https://webrevs.openjdk.org/?repo=jfx&pr=1451&range=00
  Issue: https://bugs.openjdk.org/browse/JDK-8322619
  Stats: 284 lines in 11 files changed: 213 ins; 47 del; 24 mod
  Patch: https://git.openjdk.org/jfx/pull/1451.diff
  Fetch: git fetch https://git.openjdk.org/jfx.git pull/1451/head:pull/1451

PR: https://git.openjdk.org/jfx/pull/1451