`showBeforeSizes` name resolution

[RayBenefield]

Currently the name resolution is based on the current working directory. It'd be nice to have that be a fallback, and instead prioritize the name of the outputOptions or something a little more flexible. I use this in my monorepo, and the package.json isn't reflective of all of the packages.

I may find some time to make a PR myself, but would love some thoughts on this.