inference: refine `PartialStruct` with declared method signature (#50590)
At present, in very rare cases, `PartialStruct` used for const-prop'
might have type information that's less strict than type information
that can be derived from the method's type signature, e.g.:
```julia
Base.@constprop :aggressive function refine_partial_struct((a, b)::Tuple{String,Int})
if iszero(b)
println("b=0") # to prevent semi-concrete eval
return nothing
else
return a
end
end
@test Base.return_types((AbstractString,)) do s
refine_partial_struct((s, 42))
end |> only === String
```
This commit enhances the accuracy of const-prop' by propagating `tmeet`
of `PartialStruct` and the declared type in such situations.
julia
c5e46213 - inference: refine `PartialStruct` with declared method signature (#50590)
