Add a basic model to set tile sizes + some cleanup

- compute tile sizes based on a simple model that looks at memory footprints
  (instead of using the hardcoded default value)
- adjust tile sizes to make them factors of trip counts based on an option
- update loop fusion CL options to allow setting maximal fusion at pass creation
- change an emitError to emitWarning (since it's not a hard error unless the client
  treats it that way, in which case, it can emit one)

$ mlir-opt -debug-only=loop-tile -loop-tile test/Transforms/loop-tiling.mlir

test/Transforms/loop-tiling.mlir:81:3: note: using tile sizes [4 4 5 ]

  for %i = 0 to 256 {

for %i0 = 0 to 256 step 4 {
    for %i1 = 0 to 256 step 4 {
      for %i2 = 0 to 250 step 5 {
        for %i3 = #map4(%i0) to #map11(%i0) {
          for %i4 = #map4(%i1) to #map11(%i1) {
            for %i5 = #map4(%i2) to #map12(%i2) {
              %0 = load %arg0[%i3, %i5] : memref<8x8xvector<64xf32>>
              %1 = load %arg1[%i5, %i4] : memref<8x8xvector<64xf32>>
              %2 = load %arg2[%i3, %i4] : memref<8x8xvector<64xf32>>
              %3 = mulf %0, %1 : vector<64xf32>
              %4 = addf %2, %3 : vector<64xf32>
              store %4, %arg2[%i3, %i4] : memref<8x8xvector<64xf32>>
            }
          }
        }
      }
    }
  }

PiperOrigin-RevId: 237461836