linear_algebra theory docs are outdated

Stream: general

[Eric Wieser]

Looking at https://leanprover-community.github.io/theories/linear_algebra.html, there are a bunch of links that seem to have gone dead, things like bilin_form_equiv_matrix and ring_anti_equiv.

Presumably these pages should always link to the find/... style links for symbol names to make them more resilient to module moves?

[Patrick Massot]

We should also have some kind of CI here, hunting down any dead link on the website.