Perform simplification for floor/ceil/round/trunc
Perform simplification for floor/ceil/round/trunc

- constant folding
- simplify repeated application of integer-valued functions


Former-commit-id: d2da6f0bd15e7f112d90b648a9cb36061add8c90
darkbuck/Halide,darkbuck/Halide,Trass3r/Halide,darkbuck/Halide,Trass3r/Halide,Trass3r/Halide,Trass3r/Halide,Trass3r/Halide,Trass3r/Halide,darkbuck/Halide,darkbuck/Halide,Trass3r/Halide,darkbuck/Halide,darkbuck/Halide