Implement basic dev server HTTPS certificate error detection

[kadamwhite]

This needs a spot of refactoring -- a new namespace is probably in order, at minimum -- but I've implemented an idea I discussed this morning with @shadyvb to make it more obvious when we've forgotten to accept the dev server cert. At present this only handles the Block Editor admin-side case, as we have a more reliably available notices framework in that context.

Show a notice to the user if we attempt to load a script from an HTTPS localhost address and that script encounters a loading error. This usually indicates that we forgot to accept the Webpack DevServer SSL cert.

[shadyvb]

Thanks for adding this @kadamwhite ! Saves a few minutes of confusion, and couple of clicks to approve the certificate as well! 🎉

[johnbillion]

Neat! That will save some head scratching.

You can also do this globally without the onerror attribute, I've got a branch of Query Monitor for exactly this. I'll finish it up as soon as I can.

[kadamwhite]

@johnbillion would love to compare notes on that when you get a chance, I try to global approach and it did not work as expected.
@shadyvb thanks for the review!
@ both y’all, there’s definitely room for improvement but for now I’ll land this and open a new PR for refactoring.

[shadyvb]

FYI : Chassis/chassis_openssl#4 to fix the underlying issue, after which, on Chassis projects, we can reuse the existing SSL cert and forget about this altogether.