VR underwater mask is incorrect

[alandtse]

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This is a vanilla bug. As demonstrated by this picture, there is a mask that is being rendered that is incorrect in two ways.

1. The angle of the mask does not match the water surface.
2. It isn't stereo aware and applied across the entire image so there is an eye mismatch.

This is the mask generated by ISUnderwaterMask via water.hlsl.

I have confirmed that this is only generated with partial submersion. Full submersion uses a different effect without a mask.

Here are the vertex meshes for the mask in Flat:

and in VR