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/bytes/add.rs

@@ -51,7 +51,7 @@ impl Command for BytesAdd {
             .category(Category::Bytes)
     }
 
-    fn usage(&self) -> &str {
+    fn description(&self) -> &str {
         "Add specified bytes to the input."
     }
 

crates/nu-command/src/bytes/at.rs

@@ -53,7 +53,7 @@ impl Command for BytesAt {
             .category(Category::Bytes)
     }
 
-    fn usage(&self) -> &str {
+    fn description(&self) -> &str {
         "Get bytes defined by a range."
     }
 

crates/nu-command/src/bytes/build_.rs

@@ -8,7 +8,7 @@ impl Command for BytesBuild {
         "bytes build"
     }
 
-    fn usage(&self) -> &str {
+    fn description(&self) -> &str {
         "Create bytes from the arguments."
     }
 

crates/nu-command/src/bytes/bytes_.rs

@@ -14,11 +14,11 @@ impl Command for Bytes {
             .input_output_types(vec![(Type::Nothing, Type::String)])
     }
 
-    fn usage(&self) -> &str {
+    fn description(&self) -> &str {
         "Various commands for working with byte data."
     }
 
-    fn extra_usage(&self) -> &str {
+    fn extra_description(&self) -> &str {
         "You must use one of the following subcommands. Using this command as-is will only produce this help message."
     }
 

crates/nu-command/src/bytes/collect.rs

@@ -20,7 +20,7 @@ impl Command for BytesCollect {
             .category(Category::Bytes)
     }
 
-    fn usage(&self) -> &str {
+    fn description(&self) -> &str {
         "Concatenate multiple binary into a single binary, with an optional separator between each."
     }
 

crates/nu-command/src/bytes/ends_with.rs

@@ -41,7 +41,7 @@ impl Command for BytesEndsWith {
             .category(Category::Bytes)
     }
 
-    fn usage(&self) -> &str {
+    fn description(&self) -> &str {
         "Check if bytes ends with a pattern."
     }
 

crates/nu-command/src/bytes/index_of.rs

@@ -47,7 +47,7 @@ impl Command for BytesIndexOf {
             .category(Category::Bytes)
     }
 
-    fn usage(&self) -> &str {
+    fn description(&self) -> &str {
         "Returns start index of first occurrence of pattern in bytes, or -1 if no match."
     }
 

crates/nu-command/src/bytes/length.rs

@@ -29,7 +29,7 @@ impl Command for BytesLen {
             .category(Category::Bytes)
     }
 
-    fn usage(&self) -> &str {
+    fn description(&self) -> &str {
         "Output the length of any bytes in the pipeline."
     }
 

crates/nu-command/src/bytes/remove.rs

@@ -40,7 +40,7 @@ impl Command for BytesRemove {
             .category(Category::Bytes)
     }
 
-    fn usage(&self) -> &str {
+    fn description(&self) -> &str {
         "Remove bytes."
     }
 

crates/nu-command/src/bytes/replace.rs

@@ -41,7 +41,7 @@ impl Command for BytesReplace {
             .category(Category::Bytes)
     }
 
-    fn usage(&self) -> &str {
+    fn description(&self) -> &str {
         "Find and replace binary."
     }
 

crates/nu-command/src/bytes/reverse.rs

@@ -25,7 +25,7 @@ impl Command for BytesReverse {
             .category(Category::Bytes)
     }
 
-    fn usage(&self) -> &str {
+    fn description(&self) -> &str {
         "Reverse the bytes in the pipeline."
     }
 

crates/nu-command/src/bytes/starts_with.rs

@@ -39,7 +39,7 @@ impl Command for BytesStartsWith {
             .category(Category::Bytes)
     }
 
-    fn usage(&self) -> &str {
+    fn description(&self) -> &str {
         "Check if bytes starts with a pattern."
     }