Missing stability badge for some methods in rustdoc

[Kobzol]

Some functions in the documentation generated by rustdoc (e.g. this one) are missing the stability badge. For this method, it should show 1.33.0.

[GuillaumeGomez]

This is something done on purpose as you can see here. It was implemented in #30686.

I'll send a draft to change this so we can discuss there whether or not we want this change.