Type of `@doc x` changes when REPL is loaded

[lgoettgens]

#54499 approached to fix #52986 (to no longer return nothing without REPL).
But as @ztangent and @KristofferC discussed in #52986 (comment), the returned object is still different, making tests like probcomp/Gen.jl#523 and Nemocas/AbstractAlgebra.jl#1716 fail.

IMO, an okay solution would be to add some repr (or similar) method for Base.Doc.DocStr, so that at least string(@doc x) is consistent between 1.10 and 1.11+.

[lgoettgens]

Bump. I still see it as quite a drastic change between 1.10 and 1.11 @KristofferC @JeffBezanson

[stevengj]

Note that, according to git bisect, the return type of @doc first broke in 30ccace (#51869).

[KristofferC]

I was confused about that commit because all it does is to load a package so it shouldn't do anything but alas JuliaLang/StyledStrings.jl#61