Convert from `StepRangeLen` to `StepRange` (#57521)
Currently, one may convert from a `StepRangeLen` to a `StepRange` by
using the fully parameterized constructor:
```julia
julia> r = StepRangeLen(3, 1, 4)
3:1:6
julia> StepRange{Int,Int}(r)
3:1:6
```
This PR adds a few other constructors that have fewer parameters
specified. These parameters may be derived from the argument. After this
PR, the following work:
```julia
julia> StepRange(r)
3:1:6
julia> StepRange{Int32}(r)
3:1:6
julia> StepRange{Int32}(r) |> typeof
StepRange{Int32, Int64}
```
