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-explore/src/lib.rs

@@ -9,21 +9,18 @@ mod views;
 pub use default_context::add_explore_context;
 pub use explore::Explore;
 
-use std::io;
-
 use commands::{ExpandCmd, HelpCmd, HelpManual, NuCmd, QuitCmd, TableCmd, TryCmd};
 use nu_common::{collect_pipeline, has_simple_value, CtrlC};
 use nu_protocol::{
     engine::{EngineState, Stack},
     PipelineData, Value,
 };
-use pager::{Page, Pager};
+use pager::{Page, Pager, PagerConfig, StyleConfig};
 use registry::{Command, CommandRegistry};
+use std::io;
 use terminal_size::{Height, Width};
 use views::{BinaryView, InformationView, Orientation, Preview, RecordView};
 
-use pager::{PagerConfig, StyleConfig};
-
 mod util {
     pub use super::nu_common::{create_lscolors, create_map, map_into_value};
 }