linkcheck should check URLs of raw directives

[n-peugnet]

Is your feature request related to a problem? Please describe.
When using a raw directive with the url option, the linkcheck builder does not check this URL.

Describe the solution you'd like
I would expect the URLs of raw directives to be checked by linkcheck.

[n-peugnet]

Sorry I just found out that Sphinx resolves raw directives while reading sources so an error will be displayed before the linkcheck builder is even used.

[n-peugnet]

On second thought it could still be useful to check for redirections.

[francoisfreitag]

So the suggestion is that linkcheck fails if a raw directive url attribute points to a server that issues a redirect outside of https://www.sphinx-doc.org/en/master/usage/configuration.html#confval-linkcheck_allowed_redirects?

[n-peugnet]

Yes, I implemented (and tested) it in #10757.