Set max_methods to 1 for merge/merge!/mergewith/mergewith!

[JamesWrigley]

Should prevent these invalidations seen when loading CurveFit.jl on 1.13:

inserting merge!(m::DataStructures.SortedDict{K, D, Ord}, others::AbstractDict{K, D}...) where {K, D, Ord<:Ordering} @ DataStructures ~/.julia/packages/DataStructures/qUuAY/src/sorted_dict.jl:473 invalidated:
   mt_backedges: 1: signature Tuple{typeof(merge!), Any, AbstractDict} triggered MethodInstance for Base.grow_to!(::AbstractDict{K, V}, ::Base.Generator{_A, Base.Compiler.IRShow.var"#30#31"} where _A, ::Any) where {K, V} (0 children)
                 2: signature Tuple{typeof(merge!), Any, AbstractDict} triggered MethodInstance for Base.grow_to!(::AbstractDict{K, V}, ::Base.Generator, ::Any) where {K, V} (0 children)
                 3: signature Tuple{typeof(merge!), Any, AbstractDict} triggered MethodInstance for Base.grow_to!(::AbstractDict{K, V}, ::Base.Generator, ::Any) where {K, V} (0 children)
                 4: signature Tuple{typeof(merge!), Any, AbstractDict} triggered MethodInstance for Base.grow_to!(::AbstractDict{K, V}, ::Base.Generator{I, Base.var"#Generator##0#Generator##1"{NonlinearSolveBase.Utils.var"#norm_op##2#norm_op##3"{typeof(+)}}} where I<:(Base.Iterators.Zip{Is} where Is<:Tuple{Base.AbstractBroadcasted, Base.AbstractBroadcasted}), ::Tuple{Tuple{Any, Any}, Tuple{Any, Any}}) where {K, V} (0 children)
                 5: signature Tuple{typeof(merge!), Any, AbstractDict} triggered MethodInstance for Base.grow_to!(::AbstractDict{K, V}, ::Base.Generator{_A, F} where {_A, F<:DifferentiationInterface.var"#_prepare_jacobian_aux##0#_prepare_jacobian_aux##1"}, ::Any) where {K, V} (0 children)
                 6: signature Tuple{typeof(merge!), Any, AbstractDict} triggered MethodInstance for Base.grow_to!(::AbstractDict{K, V}, ::Base.Generator{_A, F} where {_A, F<:DifferentiationInterface.var"#_prepare_jacobian_aux##12#_prepare_jacobian_aux##13"}, ::Any) where {K, V} (0 children)
                 7: signature Tuple{typeof(merge!), Any, AbstractDict} triggered MethodInstance for Base.grow_to!(::AbstractDict{K, V}, ::Base.Generator{I, Base.var"#Generator##0#Generator##1"{NonlinearSolveBase.Utils.var"#norm_op##2#norm_op##3"{typeof(+)}}} where I<:(Base.Iterators.Zip{Is} where Is<:Tuple{Base.AbstractBroadcasted, Vector{Float64}}), ::Tuple{Tuple{Any, Any}, Int64}) where {K, V} (0 children)
   backedges: 1: superseding merge!(d::AbstractDict, others::AbstractDict...) @ Base abstractdict.jl:224 with MethodInstance for merge!(::AbstractDict, ::AbstractDict) (1126 children)

inserting merge(d::OrderedCollections.OrderedDict, others::AbstractDict...) @ OrderedCollections ~/.julia/dev/OrderedCollections/src/ordered_dict.jl:488 invalidated:
   mt_backedges: <38 invalidations I deleted because they have enormous types>
   backedges: 1: superseding merge(d::AbstractDict, others::AbstractDict...) @ Base abstractdict.jl:359 with MethodInstance for merge(::AbstractDict, ::Base.Pairs{Symbol, Union{}, Nothing, @NamedTuple{}}) (21 children)
              2: superseding merge(d::AbstractDict, others::AbstractDict...) @ Base abstractdict.jl:359 with MethodInstance for merge(::AbstractDict, ::Base.Pairs{Symbol, _A, Nothing, A} where {_A, A<:NamedTuple}) (2489 children)

Partial alternative to #61329. I added mergewith() and mergewith!() to be on the safe side.

[aviatesk]

The original invalidation issue can occur generally for any package that overloads AbstractDict no matter if they implement the overload appropriately, so I believe it needs to be fixed on the Base side.
Setting @max_methods 1 may weaken inference capabilities, but the code affected by this would be type-unstable anyway, so such performance issues should generally be addressed on the package side. There is also a discussion about making @max_methods 1 the global default, which could have a significant impact on the ecosystem. However, I don't see much of a problem with introducing it in a limited fashion for code where actual issues are occurring.

[JamesWrigley]

There is also a discussion about making @max_methods 1 the global default, which could have a significant impact on the ecosystem.

That would be amazing, modulo performance hits 😅 I feel like otherwise we'll end up setting max_methods for all interface functions (like a manual version of #59091 (comment)).

[JamesWrigley]

I'll merge this in a few days if there's no objections.