Support "Functor-like" `code_typed` invocation (#57911)
This lets you easily inspect IR associated with "Functor-like" methods:
```julia
julia> (f::Foo)(offset::Float64) = f.x + f.y + offset
julia> code_typed((Foo, Float64))
1-element Vector{Any}:
CodeInfo(
1 ─ %1 = Base.getfield(f, :x)::Int64
│ %2 = Base.getfield(f, :y)::Int64
│ %3 = Base.add_int(%1, %2)::Int64
│ %4 = Base.sitofp(Float64, %3)::Float64
│ %5 = Base.add_float(%4, offset)::Float64
└── return %5
) => Float64
```
This is just a small convenience over `code_typed_by_type`, but I'm in
support of it (even though it technically changes the meaning of, e.g.,
`code_typed((1, 2))` which without this PR inspects
`(::Tuple{Int,Int})(::Vararg{Any})`
We should probably update all of our reflection machinery (`code_llvm`,
`code_lowered`, `methodinstance`, etc.) to support this "non-arg0" style
as well, but I wanted to open this first to make sure folks like it.
