RFR: 8351108: ImageIO.write(..) fails with exception when writing JPEG with IndexColorModel

[Jeremy]

Previously ImageTypeSpecifier treated all TYPE_BYTE_INDEXED as if they were opaque.

In this ticket's case: an ImageWriter received the wrong ImageTypeSpecifier and mistakenly indicated it *could* support a BufferedImage. But when the actual BufferedImage arrived (which was translucent), the ImageWriter threw an exception.

Instead:
Now the ImageTypeSpecifier accurately describes the given BufferedImage.

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Commit messages:
 - 8351108: images that are TYPE_BYTE_INDEXED can vary in translucency
 - 8351108: adding failing unit test from ticket
 - Merge branch 'openjdk:master' into master
 - Merge branch 'openjdk:master' into master
 - Merge pull request #5 from openjdk/master
 - Merge pull request #4 from openjdk/master
 - Merge pull request #3 from openjdk/master
 - Merge pull request #2 from openjdk/master
 - Merge pull request #1 from openjdk/master

Changes: https://git.openjdk.org/jdk/pull/23884/files
  Webrev: https://webrevs.openjdk.org/?repo=jdk&pr=23884&range=00
  Issue: https://bugs.openjdk.org/browse/JDK-8351108
  Stats: 85 lines in 2 files changed: 84 ins; 0 del; 1 mod
  Patch: https://git.openjdk.org/jdk/pull/23884.diff
  Fetch: git fetch https://git.openjdk.org/jdk.git pull/23884/head:pull/23884

PR: https://git.openjdk.org/jdk/pull/23884