Short-circuit reshape for Array if the result has the same shape

[jishnub]

This avoids allocating an extra Array if the reshape is a no-op.

julia> a = ones(2,2);

julia> @btime reshape($a, size($a));
  9.793 ns (1 allocation: 48 bytes)

this PR:

julia> a = ones(2,2);

julia> @btime reshape($a, size($a));
  4.534 ns (0 allocations: 0 bytes)

[adienes]

it looks like it used to be implemented this way and was intentionally changed in #56236 , ref comment

## reshape(::Array, ::Dims) returns a new Array (to avoid conditionally aliasing the structure, only the data)