Unwrap contiguous views in copyto!

[jishnub]

In copyto!(A, B) where both the arrays use linear indexing, if one or both the arrays are contiguous linear views, we may forward the copyto! to the parents. This ensures that we hit optimized copyto! implementations for the parent, if any. Similarly, for the 5-argument version. In fact, in this PR, we call the 5-argument version within the 2-argument copyto! if both the arrays use linear indexing.

An example of a performance improvement:

julia> v1 = view(rand(4000, 4000), :, :);

julia> B = similar(v1);

julia> @btime copyto!($B, $v1);
  14.257 ms (0 allocations: 0 bytes) # nightly v"1.12.0-DEV.1677"
  8.596 ms (0 allocations: 0 bytes) # this PR

In this case, we dispatch to the optimized copyto!(::Array, ::Integer, ::Array, ::Integer, ::Integer) method by unwrapping the view. This method uses memmove, which is faster than the fallback implementation that uses loops.