[llvm] [TTI]Add support for strided loads/stores. (PR #80329)

[Philip Reames via llvm-commits]

preames wrote:

For context of anyone reading along...

I asked this to be split off and intend to approve this despite the last of testing.  It is tested by the dependent SLP change, and part of my motivation for getting this in is unblocking a change I'm going to write to adjust the costs returned via the printer so that we can test this more easily.  I need the API which this change has already added for my change to make sense.  

https://github.com/llvm/llvm-project/pull/80329