isassigned for ranges with BigInt indices (#50587)
This fixes certain possible regressions in `isassigned` for ranges to
restore the 1.9-like behavior.
On v1.9
```julia
julia> r = 1:big(2)^65
1:36893488147419103232
julia> isassigned(r, lastindex(r))
true
julia> isassigned(r, true)
ERROR: ArgumentError: invalid index: true of type Bool
```
On v1.10.0-alpha1
```julia
julia> isassigned(r, lastindex(r))
ERROR: InexactError: Int64(36893488147419103232)
julia> isassigned(r, true) # Bool is converted to Int
true
julia> r[true] # but indexing with Bool doesn't work
ERROR: ArgumentError: invalid index: true of type Bool
```
This PR
```julia
julia> isassigned(r, lastindex(r))
true
julia> isassigned(r, true)
ERROR: ArgumentError: invalid index: true of type Bool
```
This still leaves
```julia
julia> isassigned(collect(1:3), true)
true
```
so that should perhaps be changed as well.
