rename nushell's cp command to cp-old making coreutils the default cp (#10678)

# Description

This PR renames nushell's `cp` command to `cp-old` to make room for
`ucp` to be renamed to `cp`, making the coreutils version of `cp` the
default for nushell. After some period of time, we should remove
`cp-old` entirely.

# User-Facing Changes
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helps us keep track of breaking changes. -->

# Tests + Formatting
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crates/nu-command/tests/commands/cp.rs

@@ -373,6 +373,7 @@ fn copy_file_and_dir_from_two_parents_up_using_multiple_dots_to_current_dir_recu
     })
 }
 
+#[ignore = "duplicate test with slight differences in ucp"]
 #[test]
 fn copy_to_non_existing_dir() {
     copy_to_non_existing_dir_impl(false);
@@ -395,6 +396,7 @@ fn copy_to_non_existing_dir_impl(progress: bool) {
     });
 }
 
+#[ignore = "duplicate test with slight differences in ucp"]
 #[test]
 fn copy_dir_contains_symlink_ignored() {
     copy_dir_contains_symlink_ignored_impl(false);
@@ -488,6 +490,7 @@ fn copy_dir_symlink_file_body_not_changed_impl(progress: bool) {
     });
 }
 
+#[ignore = "duplicate test with slight differences in ucp"]
 #[test]
 fn copy_identical_file() {
     copy_identical_file_impl(false);
@@ -530,6 +533,7 @@ fn copy_ignores_ansi_impl(progress: bool) {
     });
 }
 
+#[ignore = "duplicate test with ucp with slight differences"]
 #[test]
 fn copy_file_not_exists_dst() {
     copy_file_not_exists_dst_impl(false);
@@ -573,13 +577,12 @@ fn copy_file_with_read_permission_impl(progress: bool) {
             "cp {} valid.txt invalid_prem.txt",
             progress_flag,
         );
-        assert!(
-            actual.err.contains("invalid_prem.txt")
-                && actual.err.contains("copying to destination")
-        );
+
+        assert!(actual.err.contains("invalid_prem.txt") && actual.err.contains("denied"));
     });
 }
 
+#[ignore = "not implemented with ucp"]
 #[test]
 fn copy_file_with_update_flag() {
     copy_file_with_update_flag_impl(false);