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-lsp/src/diagnostics.rs

@@ -1,3 +1,4 @@
+use crate::LanguageServer;
 use lsp_types::{
     notification::{Notification, PublishDiagnostics},
     Diagnostic, DiagnosticSeverity, PublishDiagnosticsParams, Url,
@@ -10,8 +11,6 @@ use nu_protocol::{
     Span, Value, NU_VARIABLE_ID,
 };
 
-use crate::LanguageServer;
-
 impl LanguageServer {
     pub(crate) fn publish_diagnostics_for_file(
         &self,

crates/nu-lsp/src/lib.rs

@@ -1,13 +1,3 @@
-use std::{
-    collections::BTreeMap,
-    path::{Path, PathBuf},
-    sync::{
-        atomic::{AtomicBool, Ordering},
-        Arc,
-    },
-    time::Duration,
-};
-
 use lsp_server::{Connection, IoThreads, Message, Response, ResponseError};
 use lsp_types::{
     request::{Completion, GotoDefinition, HoverRequest, Request},
@@ -24,6 +14,15 @@ use nu_protocol::{
     DeclId, Span, Value, VarId,
 };
 use ropey::Rope;
+use std::{
+    collections::BTreeMap,
+    path::{Path, PathBuf},
+    sync::{
+        atomic::{AtomicBool, Ordering},
+        Arc,
+    },
+    time::Duration,
+};
 
 mod diagnostics;
 mod notification;