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-std/src/lib.rs

@@ -1,10 +1,11 @@
-use std::path::PathBuf;
-
 use nu_engine::{env::current_dir, eval_block};
 use nu_parser::parse;
-use nu_protocol::debugger::WithoutDebug;
-use nu_protocol::engine::{Stack, StateWorkingSet, VirtualPath};
-use nu_protocol::{report_error, PipelineData};
+use nu_protocol::{
+    debugger::WithoutDebug,
+    engine::{Stack, StateWorkingSet, VirtualPath},
+    report_error, PipelineData,
+};
+use std::path::PathBuf;
 
 // Virtual std directory unlikely to appear in user's file system
 const NU_STDLIB_VIRTUAL_DIR: &str = "NU_STDLIB_VIRTUAL_DIR";