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/platform/ansi/ansi_.rs

@@ -528,11 +528,11 @@ impl Command for AnsiCommand {
         true
     }
 
-    fn usage(&self) -> &str {
+    fn description(&self) -> &str {
         "Output ANSI codes to change color and style of text."
     }
 
-    fn extra_usage(&self) -> &str {
+    fn extra_description(&self) -> &str {
         "An introduction to what ANSI escape sequences are can be found in the
 \u{1b}]8;;https://en.wikipedia.org/wiki/ANSI_escape_code\u{1b}\\ANSI escape code\u{1b}]8;;\u{1b}\\ Wikipedia page.
 

crates/nu-command/src/platform/ansi/link.rs

@@ -35,7 +35,7 @@ impl Command for SubCommand {
             .category(Category::Platform)
     }
 
-    fn usage(&self) -> &str {
+    fn description(&self) -> &str {
         "Add a link (using OSC 8 escape sequence) to the given string."
     }
 

crates/nu-command/src/platform/ansi/strip.rs

@@ -40,7 +40,7 @@ impl Command for SubCommand {
             .category(Category::Platform)
     }
 
-    fn usage(&self) -> &str {
+    fn description(&self) -> &str {
         "Strip ANSI escape sequences from a string."
     }
 

crates/nu-command/src/platform/clear.rs

@@ -15,7 +15,7 @@ impl Command for Clear {
         "clear"
     }
 
-    fn usage(&self) -> &str {
+    fn description(&self) -> &str {
         "Clear the terminal."
     }
 

crates/nu-command/src/platform/input/input_.rs

@@ -18,7 +18,7 @@ impl Command for Input {
         "input"
     }
 
-    fn usage(&self) -> &str {
+    fn description(&self) -> &str {
         "Get input from the user."
     }
 

crates/nu-command/src/platform/input/input_listen.rs

@@ -43,11 +43,11 @@ impl Command for InputListen {
             )])
     }
 
-    fn usage(&self) -> &str {
+    fn description(&self) -> &str {
         "Listen for user interface event."
     }
 
-    fn extra_usage(&self) -> &str {
+    fn extra_description(&self) -> &str {
         r#"There are 5 different type of events: focus, key, mouse, paste, resize. Each will produce a
 corresponding record, distinguished by type field:
 ```

crates/nu-command/src/platform/input/list.rs

@@ -54,11 +54,11 @@ impl Command for InputList {
             .category(Category::Platform)
     }
 
-    fn usage(&self) -> &str {
+    fn description(&self) -> &str {
         "Interactive list selection."
     }
 
-    fn extra_usage(&self) -> &str {
+    fn extra_description(&self) -> &str {
         "Abort with esc or q."
     }
 

crates/nu-command/src/platform/is_terminal.rs

@@ -18,7 +18,7 @@ impl Command for IsTerminal {
             .category(Category::Platform)
     }
 
-    fn usage(&self) -> &str {
+    fn description(&self) -> &str {
         "Check if stdin, stdout, or stderr is a terminal."
     }
 

crates/nu-command/src/platform/kill.rs

@@ -9,7 +9,7 @@ impl Command for Kill {
         "kill"
     }
 
-    fn usage(&self) -> &str {
+    fn description(&self) -> &str {
         "Kill a process using the process id."
     }
 

crates/nu-command/src/platform/sleep.rs

@@ -15,7 +15,7 @@ impl Command for Sleep {
         "sleep"
     }
 
-    fn usage(&self) -> &str {
+    fn description(&self) -> &str {
         "Delay for a specified amount of time."
     }
 

crates/nu-command/src/platform/term_size.rs

@@ -9,7 +9,7 @@ impl Command for TermSize {
         "term size"
     }
 
-    fn usage(&self) -> &str {
+    fn description(&self) -> &str {
         "Returns a record containing the number of columns (width) and rows (height) of the terminal."
     }
 

crates/nu-command/src/platform/ulimit.rs

@@ -502,7 +502,7 @@ impl Command for ULimit {
         "ulimit"
     }
 
-    fn usage(&self) -> &str {
+    fn description(&self) -> &str {
         "Set or get resource usage limits."
     }
 

crates/nu-command/src/platform/whoami.rs

@@ -8,7 +8,7 @@ impl Command for Whoami {
         "whoami"
     }
 
-    fn usage(&self) -> &str {
+    fn description(&self) -> &str {
         "Get the current username using uutils/coreutils whoami."
     }