Add command_prelude module (#12291)

# Description
When implementing a `Command`, one must also import all the types
present in the function signatures for `Command`. This makes it so that
we often import the same set of types in each command implementation
file. E.g., something like this:
```rust
use nu_protocol::ast::Call;
use nu_protocol::engine::{Command, EngineState, Stack};
use nu_protocol::{
    record, Category, Example, IntoInterruptiblePipelineData, IntoPipelineData, PipelineData,
    ShellError, Signature, Span, Type, Value,
};
```

This PR adds the `nu_engine::command_prelude` module which contains the
necessary and commonly used types to implement a `Command`:
```rust
// command_prelude.rs
pub use crate::CallExt;
pub use nu_protocol::{
    ast::{Call, CellPath},
    engine::{Command, EngineState, Stack},
    record, Category, Example, IntoInterruptiblePipelineData, IntoPipelineData, IntoSpanned,
    PipelineData, Record, ShellError, Signature, Span, Spanned, SyntaxShape, Type, Value,
};
```

This should reduce the boilerplate needed to implement a command and
also gives us a place to track the breadth of the `Command` API. I tried
to be conservative with what went into the prelude modules, since it
might be hard/annoying to remove items from the prelude in the future.
Let me know if something should be included or excluded.

crates/nu_plugin_custom_values/src/cool_custom_value.rs

@@ -1,7 +1,6 @@
-use std::cmp::Ordering;
-
 use nu_protocol::{ast, CustomValue, ShellError, Span, Value};
 use serde::{Deserialize, Serialize};
+use std::cmp::Ordering;
 
 #[derive(Clone, Debug, PartialEq, Eq, PartialOrd, Ord, Serialize, Deserialize)]
 pub struct CoolCustomValue {

crates/nu_plugin_custom_values/src/drop_check.rs

@@ -1,3 +1,4 @@
+use crate::CustomValuePlugin;
 use nu_plugin::{EngineInterface, EvaluatedCall, SimplePluginCommand};
 use nu_protocol::{
     record, Category, CustomValue, LabeledError, PluginSignature, ShellError, Span, SyntaxShape,
@@ -5,8 +6,6 @@ use nu_protocol::{
 };
 use serde::{Deserialize, Serialize};
 
-use crate::CustomValuePlugin;
-
 #[derive(Clone, Debug, Serialize, Deserialize)]
 pub struct DropCheckValue {
     pub(crate) msg: String,

crates/nu_plugin_custom_values/src/generate.rs

@@ -1,5 +1,4 @@
 use crate::{cool_custom_value::CoolCustomValue, CustomValuePlugin};
-
 use nu_plugin::{EngineInterface, EvaluatedCall, SimplePluginCommand};
 use nu_protocol::{Category, LabeledError, PluginExample, PluginSignature, Span, Value};
 

crates/nu_plugin_custom_values/src/generate2.rs

@@ -1,5 +1,4 @@
 use crate::{second_custom_value::SecondCustomValue, CustomValuePlugin};
-
 use nu_plugin::{EngineInterface, EvaluatedCall, SimplePluginCommand};
 use nu_protocol::{
     Category, LabeledError, PluginExample, PluginSignature, Span, SyntaxShape, Value,

crates/nu_plugin_custom_values/src/update.rs

@@ -1,7 +1,6 @@
 use crate::{
     cool_custom_value::CoolCustomValue, second_custom_value::SecondCustomValue, CustomValuePlugin,
 };
-
 use nu_plugin::{EngineInterface, EvaluatedCall, SimplePluginCommand};
 use nu_protocol::{
     Category, LabeledError, PluginExample, PluginSignature, ShellError, Span, Value,

crates/nu_plugin_custom_values/src/update_arg.rs

@@ -1,5 +1,4 @@
 use crate::{update::Update, CustomValuePlugin};
-
 use nu_plugin::{EngineInterface, EvaluatedCall, SimplePluginCommand};
 use nu_protocol::{Category, LabeledError, PluginSignature, SyntaxShape, Value};