Use SHIFT-TAB to force showing method suggestions

[Liozou]

Fix #45671

Before:

julia> convert(#TAB
convert( too many methods to show )

This PR:

julia> convert(#TAB
convert( too many methods, use SHIFT-TAB to show )

julia> convert(#SHIFT-TAB
convert(::Type{AbstractChar}, x::Number) in Base at char.jl:183
convert(::Type{T}, c::T) where T<:AbstractChar in Base at char.jl:187
convert(::Type{AbstractArray{T}}, a::AbstractArray) where T in Base at abstractarray.jl:17
# etc., all methods are shown

Someone should probably check that the small gf.c diff is legal.

[KristofferC]

Why not put it back as it was before? Did anyone complain about this?

[Liozou]

I don't know, this was introduced as part of #43865.
Personally I prefer to keep the warning because I often try to TAB-complete stuff, and I'm not a big fan of having hundreds of lines blurting unexpectedly on my REPL. For the case of method completion here, I most often use it just to check at a glance whether there is a method for my argument types: if there are too many possible methods, I'd rather not see them and just try the method call. But having the possibility to see them is obviously useful in other setups, so I agree with the issue you opened, hence this PR.

[jakobnissen]

I too, would prefer showing a limited amount of methods so the REPL doesn't get flooded, with an opt-in to showing all (that is, I like this PR). No strong opinions though.

[Liozou]

CI errors look unrelated (although I didn't see the Profile error on tester_win32 elsewhere). Let me know if there is anything else I can do.

[Liozou]

Do you want to backport this to v1.8-rc2? It might make sense if you consider #45671 to be a regression compared to v1.7.