FEATURE: intersphinx--emit message during build for each objects.inv data line skipped due to regex mismatch

[bskinn]

Is your feature request related to a problem? Please describe.
This feature request is not directly related to a specific problem I'm experiencing, but it could potentially help users in debugging why an intersphinx cross-reference isn't working. The idea for this occurred to me in the course of thinking about how to handle a missing uri field from the perspective of my project for inspecting/manipulating objects.inv files, bskinn/sphobjinv.

Describe the solution you'd like
Currently, during docs build, if a line in a decompressed objects.inv does not match the regex used to parse for name, domain, etc. it is simply ignored. It would potentially be useful to have Sphinx emit an INFO message for these lines instead of silently ignoring them.

I think an INFO level message would be preferred, since implementing as a WARNING would cause difficult-to-fix breakage for anyone running with the -W flag. (They would not be able to quickly fix an objects.inv published in third-party documentation.) I think it should be easier to implement, too, since it wouldn't(?) have to be tied back into Sphinx's warning/error tracking mechanisms.

Describe alternatives you've considered
I can't think of any alternatives in terms of notifying the user during a documentation build. Other tools (e.g., sphobjinv) could implement such checking, but users would have to know to use a separate tool to discover these errors.