Make get_full_help take &dyn Command (#12903)

# Description
Changes `get_full_help` to take a `&dyn Command` instead of multiple
arguments (`&Signature`, `&Examples` `is_parser_keyword`). All of these
arguments can be gathered from a `Command`, so there is no need to pass
the pieces to `get_full_help`.

This PR also fixes an issue where the search terms are not shown if
`--help` is used on a command.

crates/nu-engine/src/documentation.rs

@@ -2,18 +2,16 @@ use crate::eval_call;
 use nu_protocol::{
     ast::{Argument, Call, Expr, Expression, RecordItem},
     debugger::WithoutDebug,
-    engine::{EngineState, Stack},
+    engine::{Command, EngineState, Stack},
     record, Category, Example, IntoPipelineData, PipelineData, Signature, Span, SyntaxShape, Type,
     Value,
 };
 use std::{collections::HashMap, fmt::Write};
 
 pub fn get_full_help(
-    sig: &Signature,
-    examples: &[Example],
+    command: &dyn Command,
     engine_state: &EngineState,
     stack: &mut Stack,
-    is_parser_keyword: bool,
 ) -> String {
     let config = engine_state.get_config();
     let doc_config = DocumentationConfig {
@@ -23,14 +21,15 @@ pub fn get_full_help(
     };
 
     let stack = &mut stack.start_capture();
+    let signature = command.signature().update_from_command(command);
 
     get_documentation(
-        sig,
-        examples,
+        &signature,
+        &command.examples(),
         engine_state,
         stack,
         &doc_config,
-        is_parser_keyword,
+        command.is_keyword(),
     )
 }
 
@@ -61,7 +60,6 @@ fn nu_highlight_string(code_string: &str, engine_state: &EngineState, stack: &mu
     code_string.to_string()
 }
 
-#[allow(clippy::cognitive_complexity)]
 fn get_documentation(
     sig: &Signature,
     examples: &[Example],

crates/nu-engine/src/eval.rs

@@ -27,18 +27,8 @@ pub fn eval_call<D: DebugContext>(
     let decl = engine_state.get_decl(call.decl_id);
 
     if !decl.is_known_external() && call.named_iter().any(|(flag, _, _)| flag.item == "help") {
-        let mut signature = engine_state.get_signature(decl);
-        signature.usage = decl.usage().to_string();
-        signature.extra_usage = decl.extra_usage().to_string();
-
-        let full_help = get_full_help(
-            &signature,
-            &decl.examples(),
-            engine_state,
-            caller_stack,
-            decl.is_keyword(),
-        );
-        Ok(Value::string(full_help, call.head).into_pipeline_data())
+        let help = get_full_help(decl, engine_state, caller_stack);
+        Ok(Value::string(help, call.head).into_pipeline_data())
     } else if let Some(block_id) = decl.block_id() {
         let block = engine_state.get_block(block_id);