sanitize.lua: A tool to extract interfaces from files

This is a simple too to remove all comments, extra whitespace and other
unnecessary things that may have creative content. What remains can be
just the minimal interface described by the header file. When used with
care, this can mechanically sanitize files, like some device tree
bindings file, that are only #defines that are meant to be used in
multiple context (the dts files and in C code to interpret the resulting
dtb).

Sponsored by: Netflix
Reviewed by: kevans
Differential Revision: https://reviews.freebsd.org/D55087