std: Standardize (input, output) param orderings

This functions swaps the order of arguments to a few functions that previously
took (output, input) parameters, but now take (input, output) parameters (in
that order).

The affected functions are:

* ptr::copy
* ptr::copy_nonoverlapping
* slice::bytes::copy_memory
* intrinsics::copy
* intrinsics::copy_nonoverlapping

Closes #22890
[breaking-change]

src/libstd/io/cursor.rs

@@ -151,7 +151,7 @@ impl Write for Cursor<Vec<u8>> {
         // there (left), and what will be appended on the end (right)
         let space = self.inner.len() - pos as usize;
         let (left, right) = buf.split_at(cmp::min(space, buf.len()));
-        slice::bytes::copy_memory(&mut self.inner[(pos as usize)..], left);
+        slice::bytes::copy_memory(left, &mut self.inner[(pos as usize)..]);
         self.inner.push_all(right);
 
         // Bump us forward