Support analyzing all source maps for a given URL

It'd be very convenient if this tool could take a URL to a webpage and give source map results for every resource found on it.

There's a couple ways to do it:

• headless chrome + puppeteer: grab all the scripts loaded on the page, fetch the code, look for source map url
• use Lighthouse with -G and load .SourceMaps from the artifacts written to disk. This is also using headless chrome, but Lighthouse does all the heavy lifting for you.