[Flow] Add patterns to convert from tensor.concat to flow.tensor.update.

[MaheshRavishankar]

These are in preparation to delay to decomposition of tensor.concat into tensor.insert_slices. This patch just adds the patterns to lower a tensor.concat along the outer dimension to flow.tensor.update. Future changes will delay the decomposition of tensor.concat to allow for non-outer dimension concatenation to be conveted into tensor.insert_slices before dispatch formation with the tensor.insert_slice fused into its producers.

Towards #19092

[benvanik]

Nice! These should be things that end up getting turned into in-place allocations for the inputs - if they don't today I'd say it's still a good change as it's just exposing the failures later on and they definitely wouldn't be turned to in-place allocations if they were left as dispatches. It'll help me prioritize finally doing better there if we have more pressure on it :)

[MaheshRavishankar]

Nice! These should be things that end up getting turned into in-place allocations for the inputs - if they don't today I'd say it's still a good change as it's just exposing the failures later on and they definitely wouldn't be turned to in-place allocations if they were left as dispatches. It'll help me prioritize finally doing better there if we have more pressure on it :)

Will have to check that. There is a chain of things here I will need to work through... sending this out in the meantime.