RFR: 8246495: Lanai: update AA clip info on GPU via compute shader

[Alexey Ushakov]

Implemented compute shader for transfering clip data in AA mode
Used MTLResourceStorageModePrivate for clipping MTLDataBuffer objects
Adjusted thread groups sizes
Reduced number of rendered objects in clip tests for more precise measurements

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Commit messages:
 - 8246495: Lanai: update AA clip info on GPU via compute shader

Changes: https://git.openjdk.java.net/lanai/pull/55/files
 Webrev: https://webrevs.openjdk.java.net/lanai/55/webrev.00
  Issue: https://bugs.openjdk.java.net/browse/JDK-8246495
  Stats: 58 lines in 6 files changed: 50 ins; 0 del; 8 mod
  Patch: https://git.openjdk.java.net/lanai/pull/55.diff
  Fetch: git fetch https://git.openjdk.java.net/lanai pull/55/head:pull/55

PR: https://git.openjdk.java.net/lanai/pull/55