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-command/src/generators/cal.rs

@@ -1,13 +1,8 @@
 use chrono::{Datelike, Local, NaiveDate};
 use indexmap::IndexMap;
 use nu_color_config::StyleComputer;
-use nu_engine::CallExt;
-use nu_protocol::ast::Call;
-use nu_protocol::engine::{Command, EngineState, Stack};
-use nu_protocol::{
-    Category, Example, IntoPipelineData, PipelineData, ShellError, Signature, Span, Spanned,
-    SyntaxShape, Type, Value,
-};
+use nu_engine::command_prelude::*;
+
 use std::collections::VecDeque;
 
 #[derive(Clone)]

crates/nu-command/src/generators/generate.rs

@@ -1,12 +1,6 @@
 use itertools::unfold;
-use nu_engine::{get_eval_block_with_early_return, CallExt};
-
-use nu_protocol::{
-    ast::Call,
-    engine::{Closure, Command, EngineState, Stack},
-    Category, Example, IntoInterruptiblePipelineData, IntoPipelineData, PipelineData, ShellError,
-    Signature, Span, Spanned, SyntaxShape, Type, Value,
-};
+use nu_engine::{command_prelude::*, get_eval_block_with_early_return};
+use nu_protocol::engine::Closure;
 
 #[derive(Clone)]
 pub struct Generate;

crates/nu-command/src/generators/seq.rs

@@ -1,10 +1,4 @@
-use nu_engine::CallExt;
-use nu_protocol::{
-    ast::Call,
-    engine::{Command, EngineState, Stack},
-    Category, Example, PipelineData, ShellError, Signature, Span, Spanned, SyntaxShape, Type,
-    Value,
-};
+use nu_engine::command_prelude::*;
 
 #[derive(Clone)]
 pub struct Seq;

crates/nu-command/src/generators/seq_char.rs

@@ -1,9 +1,4 @@
-use nu_engine::CallExt;
-use nu_protocol::engine::{Command, EngineState, Stack};
-use nu_protocol::{
-    ast::Call, Category, Example, IntoPipelineData, PipelineData, ShellError, Signature, Span,
-    Spanned, SyntaxShape, Type, Value,
-};
+use nu_engine::command_prelude::*;
 
 #[derive(Clone)]
 pub struct SeqChar;

crates/nu-command/src/generators/seq_date.rs

@@ -1,12 +1,6 @@
-use chrono::naive::NaiveDate;
-use chrono::{Duration, Local};
-use nu_engine::CallExt;
-use nu_protocol::ast::Call;
-use nu_protocol::engine::{Command, EngineState, Stack};
-use nu_protocol::{
-    Category, Example, IntoPipelineData, PipelineData, ShellError, Signature, Span, Spanned,
-    SyntaxShape, Type, Value,
-};
+use chrono::{Duration, Local, NaiveDate};
+use nu_engine::command_prelude::*;
+
 use std::fmt::Write;
 
 #[derive(Clone)]