Accept more general Integer sizes in reshape (#55521)
This PR generalizes the `reshape` methods to accept `Integer`s instead
of `Int`s, and adds a `_reshape_uncolon` method for `Integer` arguments.
The current `_reshape_uncolon` method that accepts `Int`s is left
unchanged to ensure that the inferred types are not impacted. I've also
tried to ensure that most `Integer` subtypes in `Base` that may be
safely converted to `Int`s pass through that method.
The call sequence would now go like this:
```julia
reshape(A, ::Tuple{Vararg{Union{Integer, Colon}}}) -> reshape(A, ::Tuple{Vararg{Integer}}) -> reshape(A, ::Tuple{Vararg{Int}}) (fallback)
```
This lets packages define `reshape(A::CustomArray, ::Tuple{Integer,
Vararg{Integer}})` without having to implement `_reshape_uncolon` by
themselves (or having to call internal `Base` functions, as in
https://github.com/JuliaArrays/FillArrays.jl/issues/373). `reshape`
calls involving a `Colon` would convert this to an `Integer` in `Base`,
and then pass the `Integer` sizes to the custom method defined in the
package.
This PR does not resolve issues like
https://github.com/JuliaLang/julia/issues/40076 because this still
converts `Integer`s to `Int`s in the actual reshaping step. However,
`BigInt` sizes that may be converted to `Int`s will work now:
```julia
julia> reshape(1:4, big(2), big(2))
2×2 reshape(::UnitRange{Int64}, 2, 2) with eltype Int64:
1 3
2 4
julia> reshape(1:4, big(1), :)
1×4 reshape(::UnitRange{Int64}, 1, 4) with eltype Int64:
1 2 3 4
```
Note that the reshape method with `Integer` sizes explicitly converts
these to `Int`s to avoid self-recursion (as opposed to calling
`to_shape` to carry out the conversion implicitly). In the future, we
may want to decide what to do with types or values that can't be
converted to an `Int`.
---------
Co-authored-by: Neven Sajko <s@purelymail.com>
