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.

src/command.rs

@@ -1,12 +1,9 @@
-use nu_engine::{get_full_help, CallExt};
-use nu_parser::parse;
-use nu_parser::{escape_for_script_arg, escape_quote_string};
-use nu_protocol::report_error;
+use nu_engine::{command_prelude::*, get_full_help};
+use nu_parser::{escape_for_script_arg, escape_quote_string, parse};
 use nu_protocol::{
-    ast::{Call, Expr, Expression},
-    engine::{Command, EngineState, Stack, StateWorkingSet},
-    Category, Example, IntoPipelineData, PipelineData, ShellError, Signature, Spanned, SyntaxShape,
-    Value,
+    ast::{Expr, Expression},
+    engine::StateWorkingSet,
+    report_error,
 };
 use nu_utils::stdout_write_all_and_flush;