fix performance in printf

[KristofferC]

Same story as in #28661.

Improves the benchmark in print_to_file (that we show on the benchmark plot on the homepage).

julia> using Printf

julia> function printfd(n)
           open("/dev/null", "w") do io
               for i = 1:n
                   @printf(io, "%d %d\n", i, i + 1)
               end
           end
       end

Before

julia> @btime printfd(1000)
  117.889 μs (5 allocations: 400 bytes)

After

julia> @btime printfd(1000)
  74.283 μs (5 allocations: 400 bytes)

[JeffBezanson]

I don't think this is always in bounds --- digits is a fixed size and it seems to be possible to ask for enough digits to overflow it.

[KristofferC]

Ok let's remove the inbounds.

[PallHaraldsson]

Good to get the speed-up, while Int('0')+(x&0x7) seems to do the same, without less self-documenting 48 [ASCII code].