Add shape function SingleImageRandomDotStereograms (#15431)

* Add shape function SingleImageRandomDotStereograms

This fix tries to address the issue raised in 15429 where
there is no shape function for SingleImageRandomDotStereograms.

This fix adds the shape function for `SingleImageRandomDotStereograms`.

NOTE: `SingleImageRandomDotStereograms` takes an attribute
of `output_image_shape` which is in the format of
`[X, Y, C]` (`[ImageX, ImageY, Channel]`. However, the actual
data output is in the format of
`[ImageY, ImageX, Channel]` (`[h, w, c]`)
so by default the output_image_shape has the value
of [1024, 768, 1] but the output data will be [768, 1024, 1].
And if `[1200, 800, 1]` is used explicitly then the output
data shape will be `[800, 1200, 1]`.

This fix does not change the behavior for now.

This fix fixes 15429.

Signed-off-by: Yong Tang <yong.tang.github@outlook.com>

* Add test cases for shape function for SingleImageRandomDotStereograms

Signed-off-by: Yong Tang <yong.tang.github@outlook.com>

* Update Bazel BUILD file

Signed-off-by: Yong Tang <yong.tang.github@outlook.com>

* Address review feedback.

Signed-off-by: Yong Tang <yong.tang.github@outlook.com>