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_plugin_query/src/query.rs

@@ -12,10 +12,6 @@ impl Query {
     pub fn new() -> Self {
         Default::default()
     }
-
-    pub fn usage() -> &'static str {
-        "Usage: query"
-    }
 }
 
 impl Plugin for Query {
@@ -44,7 +40,7 @@ impl SimplePluginCommand for QueryCommand {
         "query"
     }
 
-    fn usage(&self) -> &str {
+    fn description(&self) -> &str {
         "Show all the query commands"
     }
 

crates/nu_plugin_query/src/query_json.rs

@@ -12,7 +12,7 @@ impl SimplePluginCommand for QueryJson {
         "query json"
     }
 
-    fn usage(&self) -> &str {
+    fn description(&self) -> &str {
         "execute json query on json file (open --raw <file> | query json 'query string')"
     }
 

crates/nu_plugin_query/src/query_web.rs

@@ -14,7 +14,7 @@ impl SimplePluginCommand for QueryWeb {
         "query web"
     }
 
-    fn usage(&self) -> &str {
+    fn description(&self) -> &str {
         "execute selector query on html/web"
     }
 

crates/nu_plugin_query/src/query_webpage_info.rs

@@ -12,7 +12,7 @@ impl SimplePluginCommand for QueryWebpageInfo {
         "query webpage-info"
     }
 
-    fn usage(&self) -> &str {
+    fn description(&self) -> &str {
         "uses the webpage crate to extract info from html: title, description, language, links, RSS feeds, Opengraph, Schema.org, and more"
     }
 

crates/nu_plugin_query/src/query_xml.rs

@@ -15,7 +15,7 @@ impl SimplePluginCommand for QueryXml {
         "query xml"
     }
 
-    fn usage(&self) -> &str {
+    fn description(&self) -> &str {
         "execute xpath query on xml"
     }