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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crates/nu-command/src/filesystem/cp.rs

@@ -31,11 +31,11 @@ pub struct Cp;
 
 impl Command for Cp {
     fn name(&self) -> &str {
-        "cp"
+        "cp-old"
     }
 
     fn usage(&self) -> &str {
-        "Copy files."
+        "Old nushell version of Copy files."
     }
 
     fn search_terms(&self) -> Vec<&str> {
@@ -43,7 +43,7 @@ impl Command for Cp {
     }
 
     fn signature(&self) -> Signature {
-        Signature::build("cp")
+        Signature::build("cp-old")
             .input_output_types(vec![(Type::Nothing, Type::Nothing)])
             .required("source", SyntaxShape::GlobPattern, "the place to copy from")
             .required("destination", SyntaxShape::Filepath, "the place to copy to")

crates/nu-command/src/filesystem/ucp.rs

@@ -27,7 +27,7 @@ pub struct UCp;
 
 impl Command for UCp {
     fn name(&self) -> &str {
-        "ucp"
+        "cp"
     }
 
     fn usage(&self) -> &str {
@@ -39,7 +39,7 @@ impl Command for UCp {
     }
 
     fn signature(&self) -> Signature {
-        Signature::build("ucp")
+        Signature::build("cp")
             .input_output_types(vec![(Type::Nothing, Type::Nothing)])
             .switch("recursive", "copy directories recursively", Some('r'))
             .switch("verbose", "explicitly state what is being done", Some('v'))
@@ -63,22 +63,22 @@ impl Command for UCp {
         vec![
             Example {
                 description: "Copy myfile to dir_b",
-                example: "ucp myfile dir_b",
+                example: "cp myfile dir_b",
                 result: None,
             },
             Example {
                 description: "Recursively copy dir_a to dir_b",
-                example: "ucp -r dir_a dir_b",
+                example: "cp -r dir_a dir_b",
                 result: None,
             },
             Example {
                 description: "Recursively copy dir_a to dir_b, and print the feedbacks",
-                example: "ucp -r -v dir_a dir_b",
+                example: "cp -r -v dir_a dir_b",
                 result: None,
             },
             Example {
                 description: "Move many files into a directory",
-                example: "ucp *.txt dir_a",
+                example: "cp *.txt dir_a",
                 result: None,
             },
         ]