RunGen: allow for chunky/interleaved inputs
RunGen: allow for chunky/interleaved inputs

Main change is to add smarts to run inputs thru BoundsQuery as well, and copy them to a different-layout Buffer if necessary. Also a bit of drive-by cleanup to move more code out of main(), and add a flag to allow customizing the number of warmup iterations for benchmarking.

psuriana/Halide,psuriana/Halide,kgnk/Halide,kgnk/Halide,psuriana/Halide,kgnk/Halide,psuriana/Halide,kgnk/Halide,kgnk/Halide,psuriana/Halide,kgnk/Halide,kgnk/Halide,psuriana/Halide,kgnk/Halide,psuriana/Halide