last(::Tuple) should be type stable

[dlfivefifty]

This caught me by surprise:

julia> x=(1,2.0,"hi");

julia> @code_warntype first(x)
Variables:
  #self#::Base.#first
  t::Tuple{Int64,Float64,String}

Body:
  begin 
      return (Base.getfield)(t::Tuple{Int64,Float64,String},1)::Int64
  end::Int64

julia> @code_warntype(last(x))
Variables:
  #self#::Base.#last
  a::Tuple{Int64,Float64,String}

Body:
  begin 
      SSAValue(0) = (Base.nfields)(a::Tuple{Int64,Float64,String})::Int64
      return (Base.getfield)(a::Tuple{Int64,Float64,String},SSAValue(0))::Union{Float64,Int64,String}
  end::Union{Float64,Int64,String}

[Sacha0]

#19540

[JeffBezanson]

fixed by #19605.