Implement parametric tiling on standard for loops

Implement parametric tiling on standard for loops

Parametric tiling can be used to extract outer loops with fixed number of
iterations.  This in turn enables mapping to GPU kernels on a fixed grid
independently of the range of the original loops, which may be unknown
statically, making the kernel adaptable to different sizes.  Provide a utility
function that also computes the parametric tile size given the range of the
loop.  Exercise the utility function through a simple pass that applies it to
all top-level loop nests.  Permutability or parallelism checks must be
performed before calling this utility function in actual passes.

Note that parametric tiling cannot be implemented in a purely affine way,
although it can be encoded using semi-affine maps.  The choice to implement it
on standard loops is guided by them being the common representation between
Affine loops, Linalg and GPU kernels.

PiperOrigin-RevId: 257180251