RFR: 8256331 Lanai: DrawImage/IncorrectAlphaSurface2SW fails

[Alexey Ushakov]

Added conversion from argb_pre after reading pixels
Reverted applying alpha in shader

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Commit messages:
 - 8256331 Lanai: DrawImage/IncorrectAlphaSurface2SW fails

Changes: https://git.openjdk.java.net/lanai/pull/129/files
 Webrev: https://webrevs.openjdk.java.net/?repo=lanai&pr=129&range=00
  Issue: https://bugs.openjdk.java.net/browse/JDK-8256331
  Stats: 25 lines in 4 files changed: 13 ins; 7 del; 5 mod
  Patch: https://git.openjdk.java.net/lanai/pull/129.diff
  Fetch: git fetch https://git.openjdk.java.net/lanai pull/129/head:pull/129

PR: https://git.openjdk.java.net/lanai/pull/129