[mlir][Vector] Add lowering of 1-D vector transfer_read/write to masked load/store

[nicolasvasilache]

Summary

This revision adds support to lower 1-D vector transfers to LLVM.
A mask of the vector length is created that compares the base offset + linear index to the dim of the vector.
In each position where this does not overflow (i.e. offset + vector index < dim), the mask is set to 1.

A notable fact is that the lowering uses llvm.dialect_cast to allow writing code in the simplest form by targeting the simplest mix of vector and LLVM dialects and
letting other conversions kick in.

[nicolasvasilache]

Make test more legible.

[aartbik]

mlir/lib/Conversion/StandardToLLVM/StandardToLLVM.cpp

788

this was of course already there before you moved, but it just caught my eye

I am guessing we are doing this to avoid compiler errors in non-debug mode (successStrides not used) . Are there any plans to make the compiler smarter about uses in asserts? It seems a bit strange to add code like this just to suppress those?