Scaladoc: possibility to verify links in docs

[KacperFKorban]

Scaladoc should be able to verify the correctness of links in docstrings and static sites.

Motivation: It's hard to check the correctness of links manually when changing the documentation.
e.g.

https://dotty.epfl.ch/api/scala/runtime/stdLibPatches/language$$unsafeNulls$.html# points to http://dotty.epfl.ch/docs/reference/other-new-features/explicit-nulls.html which has been moved to https://dotty.epfl.ch/docs/reference/experimental/explicit-nulls.html

We should be able to detect incorrect links (usually pointing to 404) when generating scaladoc.

Some thoughts:

• This should be under a flag possibly, since making HTTP calls should definitely not be a default behavior for a doctool
• We should detect changes in the static site inside of the same repo

[Dedelweiss]

Hello @szymon-rd, I saw that you are currently assigned to this issue. I have started working on this problem and I just wanted to know if you had started anything?

[szymon-rd]

Hi, no, I did not start working on it.