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_query/src/query.rs

@@ -1,7 +1,4 @@
-use crate::query_json::QueryJson;
-use crate::query_web::QueryWeb;
-use crate::query_xml::QueryXml;
-
+use crate::{query_json::QueryJson, query_web::QueryWeb, query_xml::QueryXml};
 use nu_plugin::{EvaluatedCall, Plugin, PluginCommand, SimplePluginCommand};
 use nu_protocol::{Category, LabeledError, PluginSignature, Value};
 

crates/nu_plugin_query/src/query_json.rs

@@ -1,11 +1,10 @@
+use crate::Query;
 use gjson::Value as gjValue;
 use nu_plugin::{EngineInterface, EvaluatedCall, SimplePluginCommand};
 use nu_protocol::{
     Category, LabeledError, PluginSignature, Record, Span, Spanned, SyntaxShape, Value,
 };
 
-use crate::Query;
-
 pub struct QueryJson;
 
 impl SimplePluginCommand for QueryJson {

crates/nu_plugin_query/src/query_xml.rs

@@ -1,3 +1,4 @@
+use crate::Query;
 use nu_plugin::{EngineInterface, EvaluatedCall, SimplePluginCommand};
 use nu_protocol::{
     record, Category, LabeledError, PluginSignature, Record, Span, Spanned, SyntaxShape, Value,
@@ -5,8 +6,6 @@ use nu_protocol::{
 use sxd_document::parser;
 use sxd_xpath::{Context, Factory};
 
-use crate::Query;
-
 pub struct QueryXml;
 
 impl SimplePluginCommand for QueryXml {