We already removed it from the online docs with #35132.
Currently it can only be "Built-In Types" (Variant types) or "Core"
(everything else), which is of limited use.
We might also want to consider dropping it from `ClassDB` altogether
in Godot 4.0.
Follow-up to #31925, `<member />` tags just before `</members>` would cause
a parsing issue, and we'd never notice that we're no longer parsing members.
Also added space before closing `/>`.
In many of the XML files it had been noted that when the documentation
refers to a return value, both "Return" and "Returns" are used. This
has now been fixed to only say "Returns".
Fixes#28867
