[Flow] Extend CollapseDimensionsPass (iree-org#17993)

iree-flow-collapse-dimensions is currently very limited. The pass doens't
support propagating collapse of dimensions through multiple operations.
This adds support to collapsing dimensions through chains of operations, 
which should allow for better codegen at the smaller dimensionality.

Also, this will need to be disabled in the specific case of softmax
fusion since there is a backend bug
(iree-org#17948).

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Signed-off-by: Ian Wood <ianwood2024@u.northwestern.edu>