FYI: 8233305: Implement rendering to volatile image

[Alexey Ushakov]

Implemented MTLBlitLoops_SurfaceToSwBlit
Flushed rendering content to get correct result from VI.getSnapshot()

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Commit messages:
 - 8233305: Implement rendering to volatile image

Changes: https://git.openjdk.java.net/lanai/pull/23/files
 Webrev: https://webrevs.openjdk.java.net/lanai/23/webrev.00
  Issue: https://bugs.openjdk.java.net/browse/JDK-8233305
  Stats: 268 lines in 10 files changed: 243 ins; 9 del; 16 mod
  Patch: https://git.openjdk.java.net/lanai/pull/23.diff
  Fetch: git fetch https://git.openjdk.java.net/lanai pull/23/head:pull/23

PR: https://git.openjdk.java.net/lanai/pull/23