Refactor LowerAffineApply

In LoweringUtils, extract out `expandAffineMap`.  This function takes an affine
map and a list of values the map should be applied to and emits a sequence of
arithmetic instructions that implement the affine map.  It is independent of
the AffineApplyOp and can be used in places where we need to insert an
evaluation of an affine map without relying on a (temporary) `affine_apply`
instruction.  This prepares for a merge between LowerAffineApply and
LowerForAndIf passes.

Move the `expandAffineApply` function to the LowerAffineApply pass since it is
the only place that must be aware of the `affine_apply` instructions.

PiperOrigin-RevId: 227563439