RFR: 8297676: DataBuffer.TYPE_SHORT/TYPE_FLOAT/TYPE_DOUBLE are not placeholders

[Sergey Bylokhov]

The specification for the DataBuffer.TYPE_SHORT/TYPE_FLOAT/TYPE_DOUBLE mentioned that all of them are "Placeholder for future use" which is not true.

They are used and it is possible to create the ComponentColorModel for each of this transferType. Also, there is a specific data buffer for each: [DataBufferFloat](https://github.com/openjdk/jdk/blob/master/src/java.desktop/share/classes/java/awt/image/DataBufferFloat.java#L67), [DataBufferDouble](https://github.com/openjdk/jdk/blob/master/src/java.desktop/share/classes/java/awt/image/DataBufferDouble.java#L67), and [DataBufferShort](https://github.com/openjdk/jdk/blob/master/src/java.desktop/share/classes/java/awt/image/DataBufferShort.java#L74).

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Commit messages:
 - 8297676: DataBuffer.TYPE_SHORT/TYPE_FLOAT/TYPE_DOUBLE are not placeholders

Changes: https://git.openjdk.org/jdk/pull/11374/files
 Webrev: https://webrevs.openjdk.org/?repo=jdk&pr=11374&range=00
  Issue: https://bugs.openjdk.org/browse/JDK-8297676
  Stats: 10 lines in 1 file changed: 2 ins; 2 del; 6 mod
  Patch: https://git.openjdk.org/jdk/pull/11374.diff
  Fetch: git fetch https://git.openjdk.org/jdk pull/11374/head:pull/11374

PR: https://git.openjdk.org/jdk/pull/11374