Determine CSP `script-src` values automatically for inline scripts based on currently built/deployed index.html

[caugner]

Ultimately, what we should do is to generate and add a script-src item automatically for each inline script in the currently built index.html, and (for stage/prod builds) additionally an entry for each inline script in the currently deployed index.html.

Originally posted by @caugner in mdn/yari#6992 (comment)

[caugner]

This would still be nice, moving to Dex.