Previously, multisampled images used the 'depth' member of 3D images
or 2D arrays as the number of samples. This caused rendering to a
layer of a 2D array to be interpreted as rendering to a multisampled
render target. This change adds a 'samples' member which is orthogonal
to 'depth'.

Note that write operations put the same color into each of the samples,
while read operations (still) assume multisampled images have been
resolved into the first slice.

Change-Id: Ib33a0cf8194e19fcbb569b0c257ba1e1bd9c4821
Reviewed-on: https://swiftshader-review.googlesource.com/14808Tested-by: Nicolas Capens <nicolascapens@google.com>
Reviewed-by: Alexis Hétu <sugoi@google.com>
Reviewed-by: Nicolas Capens <nicolascapens@google.com>