[compiler][snap] Fixes to relative path resolution; compile subcommand (#35688)

More snap improvements for use with agents:
* `yarn snap compile [--debug] <path>` for compiling any file,
optionally with debug logs
* `yarn snap minimize <path>` now accepts path as a positional param for
consistency w 'compile' command
* Both compile/minimize commands properly handle paths relative to the
compiler/ directory. When using `yarn snap` the current working
directory is compiler/packages/snap, but you're generally running it
from the compiler directory so this matches expectations of callers
better.