<AWT Dev> RFR: 8266079: Lanai: AlphaComposite shows differences on Metal compared to OpenGL [v2]

[Alexey Ushakov]

> Set black color for underlying window background to perform correct blending operations in metal with window surface destination

Alexey Ushakov has updated the pull request with a new target base due to a merge or a rebase. The pull request now contains one commit:

  8266079: Lanai: AlphaComposite shows differences on Metal compared to OpenGL
  
  Implemented blit via compute kernel

-------------

Changes: https://git.openjdk.java.net/jdk/pull/4206/files
 Webrev: https://webrevs.openjdk.java.net/?repo=jdk&pr=4206&range=01
  Stats: 289 lines in 4 files changed: 288 ins; 0 del; 1 mod
  Patch: https://git.openjdk.java.net/jdk/pull/4206.diff
  Fetch: git fetch https://git.openjdk.java.net/jdk pull/4206/head:pull/4206

PR: https://git.openjdk.java.net/jdk/pull/4206