Change the usage misnomer to "description" (#13598)

# Description
    
The meaning of the word usage is specific to describing how a command
function is *used* and not a synonym for general description. Usage can
be used to describe the SYNOPSIS or EXAMPLES sections of a man page
where the permitted argument combinations are shown or example *uses*
are given.
Let's not confuse people and call it what it is a description.

Our `help` command already creates its own *Usage* section based on the
available arguments and doesn't refer to the description with usage.

# User-Facing Changes

`help commands` and `scope commands` will now use `description` or
`extra_description`
`usage`-> `description`
`extra_usage` -> `extra_description`

Breaking change in the plugin protocol:

In the signature record communicated with the engine.
`usage`-> `description`
`extra_usage` -> `extra_description`

The same rename also takes place for the methods on
`SimplePluginCommand` and `PluginCommand`

# Tests + Formatting
- Updated plugin protocol specific changes
# After Submitting
- [ ] update plugin protocol doc

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

@@ -10,7 +10,7 @@ impl Command for Cd {
         "cd"
     }
 
-    fn usage(&self) -> &str {
+    fn description(&self) -> &str {
         "Change directory."
     }
 

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

@@ -27,7 +27,7 @@ impl Command for Du {
         "du"
     }
 
-    fn usage(&self) -> &str {
+    fn description(&self) -> &str {
         "Find disk usage sizes of specified items."
     }
 

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

@@ -44,7 +44,7 @@ impl Command for Glob {
             .category(Category::FileSystem)
     }
 
-    fn usage(&self) -> &str {
+    fn description(&self) -> &str {
         "Creates a list of files and/or folders based on the glob pattern provided."
     }
 
@@ -114,7 +114,7 @@ impl Command for Glob {
         ]
     }
 
-    fn extra_usage(&self) -> &str {
+    fn extra_description(&self) -> &str {
         r#"For more glob pattern help, please refer to https://docs.rs/crate/wax/latest"#
     }
 

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

@@ -38,7 +38,7 @@ impl Command for Ls {
         "ls"
     }
 
-    fn usage(&self) -> &str {
+    fn description(&self) -> &str {
         "List the filenames, sizes, and modification times of items in a directory."
     }
 

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

@@ -10,7 +10,7 @@ impl Command for Mktemp {
         "mktemp"
     }
 
-    fn usage(&self) -> &str {
+    fn description(&self) -> &str {
         "Create temporary files or directories using uutils/coreutils mktemp."
     }
 

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

@@ -18,11 +18,11 @@ impl Command for Open {
         "open"
     }
 
-    fn usage(&self) -> &str {
+    fn description(&self) -> &str {
         "Load a file into a cell, converting to table if possible (avoid by appending '--raw')."
     }
 
-    fn extra_usage(&self) -> &str {
+    fn extra_description(&self) -> &str {
         "Support to automatically parse files with an extension `.xyz` can be provided by a `from xyz` command in scope."
     }
 

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

@@ -25,7 +25,7 @@ impl Command for Rm {
         "rm"
     }
 
-    fn usage(&self) -> &str {
+    fn description(&self) -> &str {
         "Remove files and directories."
     }
 

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

@@ -22,7 +22,7 @@ impl Command for Save {
         "save"
     }
 
-    fn usage(&self) -> &str {
+    fn description(&self) -> &str {
         "Save a file."
     }
 

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

@@ -15,7 +15,7 @@ impl Command for Start {
         "start"
     }
 
-    fn usage(&self) -> &str {
+    fn description(&self) -> &str {
         "Open a folder, file or website in the default application or viewer."
     }
 

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

@@ -51,7 +51,7 @@ impl Command for Touch {
             .category(Category::FileSystem)
     }
 
-    fn usage(&self) -> &str {
+    fn description(&self) -> &str {
         "Creates one or more files."
     }
 

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

@@ -20,7 +20,7 @@ impl Command for UCp {
         "cp"
     }
 
-    fn usage(&self) -> &str {
+    fn description(&self) -> &str {
         "Copy files using uutils/coreutils cp."
     }
 

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

@@ -28,7 +28,7 @@ impl Command for UMkdir {
         "mkdir"
     }
 
-    fn usage(&self) -> &str {
+    fn description(&self) -> &str {
         "Create directories, with intermediary directories if required using uutils/coreutils mkdir."
     }
 

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

@@ -14,7 +14,7 @@ impl Command for UMv {
         "mv"
     }
 
-    fn usage(&self) -> &str {
+    fn description(&self) -> &str {
         "Move files or directories using uutils/coreutils mv."
     }
 

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

@@ -28,7 +28,7 @@ impl Command for Watch {
         "watch"
     }
 
-    fn usage(&self) -> &str {
+    fn description(&self) -> &str {
         "Watch for file changes and execute Nu code when they happen."
     }