Add Compilation Modes Setting

[bscan]

Currently, the raku source is compiled using nqp::getcomp. This could run BEGIN and CHECK blocks, but a regex strips these phasers out. This should ideally be controlled by a setting. Some people may want to run these blocks (e.g. BEGIN block being required to set a path). This would also be the first of multiple compilation "modes" if we identify other methods of parsing.