Use CommandType in more places (#12832)

# Description
Kind of a vague title, but this PR does two main things:
1. Rather than overriding functions like `Command::is_parser_keyword`,
this PR instead changes commands to override `Command::command_type`.
The `CommandType` returned by `Command::command_type` is then used to
automatically determine whether `Command::is_parser_keyword` and the
other `is_{type}` functions should return true. These changes allow us
to remove the `CommandType::Other` case and should also guarantee than
only one of the `is_{type}` functions on `Command` will return true.
2. Uses the new, reworked `Command::command_type` function in the `scope
commands` and `which` commands.


# User-Facing Changes
- Breaking change for `scope commands`: multiple columns (`is_builtin`,
`is_keyword`, `is_plugin`, etc.) have been merged into the `type`
column.
- Breaking change: the `which` command can now report `plugin` or
`keyword` instead of `built-in` in the `type` column. It may also now
report `external` instead of `custom` in the `type` column for known
`extern`s.

crates/nu-cli/src/commands/keybindings.rs

@@ -42,7 +42,7 @@ For more information on input and keybindings, check:
                 &Keybindings.examples(),
                 engine_state,
                 stack,
-                self.is_parser_keyword(),
+                self.is_keyword(),
             ),
             call.head,
         )

crates/nu-cli/src/menus/help_completions.rs

@@ -18,7 +18,7 @@ impl NuHelpCompleter {
         //Vec<(Signature, Vec<Example>, bool, bool)> {
         let mut commands = full_commands
             .iter()
-            .filter(|(sig, _, _, _, _)| {
+            .filter(|(sig, _, _)| {
                 sig.name.to_folded_case().contains(&folded_line)
                     || sig.usage.to_folded_case().contains(&folded_line)
                     || sig
@@ -29,7 +29,7 @@ impl NuHelpCompleter {
             })
             .collect::<Vec<_>>();
 
-        commands.sort_by(|(a, _, _, _, _), (b, _, _, _, _)| {
+        commands.sort_by(|(a, _, _), (b, _, _)| {
             let a_distance = levenshtein_distance(line, &a.name);
             let b_distance = levenshtein_distance(line, &b.name);
             a_distance.cmp(&b_distance)
@@ -37,7 +37,7 @@ impl NuHelpCompleter {
 
         commands
             .into_iter()
-            .map(|(sig, examples, _, _, _)| {
+            .map(|(sig, examples, _)| {
                 let mut long_desc = String::new();
 
                 let usage = &sig.usage;