Add range(start, stop, length)

[mkitti]

This is a minimal implementation of range(start, stop, length) with no fuss. It adds the three positional argument version. One or two positional arguments are still disallowed.

Closes #38750

# The one line of actual code added is literally the one line below
julia> Base.range(start, stop, length::Union{Integer,Nothing}) = Base._range(start, nothing, stop, length)

julia> range(1,5,5)
1.0:1.0:5.0

julia> range(1,5,2)
1.0:4.0:5.0

julia> range(1,5)
ERROR: ArgumentError: At least one of `length` or `step` must be specified
Stacktrace:
 [1] _range2(::Int64, ::Nothing, ::Int64, ::Nothing) at .\range.jl:97
 [2] range(::Int64, ::Int64; length::Nothing, step::Nothing) at .\range.jl:94
 [3] range(::Int64, ::Int64) at .\range.jl:94
 [4] top-level scope at REPL[4]:1
 
 julia> range(5)
ERROR: ArgumentError: At least one of `length` or `stop` must be specified
Stacktrace:
 [1] _range(::Int64, ::Nothing, ::Nothing, ::Nothing) at .\range.jl:126
 [2] range(::Int64; length::Nothing, stop::Nothing, step::Nothing) at .\range.jl:91
 [3] range(::Int64) at .\range.jl:91
 [4] top-level scope at REPL[5]:1

While I still think we should evaluate the larger picture, there are compatible alternatives I would like to explore such as using Pair to represent start => stop, resulting in unambiguous syntax. My approach to that depends on if this is integrated or not.

[mkitti]

See 👍🏻 in #38750 (comment) by @StefanKarpinski

[mkitti]

Closing for now with deference to comments in #38750 and #38041. I can rebase later if issues are still not resolved.