bevy_ecs/system/commands/ folder docs pass (#18639)

- Lots of nits, formatting, and rephrasing, with the goal of making
things more consistent.
- Fix outdated error handler explanation in `Commands` and
`EntityCommands` docs.
- Expand docs for system-related commands.
- Remove panic notes if the command only panics with the default error
handler.
- Update error handling notes for `try_` variants.
- Hide `prelude` import in most doctest examples, unless the example
uses something that people might not realize is in the prelude (like
`Name`).
- Remove a couple doctest examples that (in my opinion) didn't make
sense.

---------

Co-authored-by: Alice Cecile <alice.i.cecile@gmail.com>
Co-authored-by: Chris Russell <8494645+chescock@users.noreply.github.com>

crates/bevy_ecs/src/system/commands/command.rs

@@ -1,5 +1,5 @@
-//! This module contains the definition of the [`Command`] trait, as well as
-//! blanket implementations of the trait for closures.
+//! Contains the definition of the [`Command`] trait,
+//! as well as the blanket implementation of the trait for closures.
 //!
 //! It also contains functions that return closures for use with
 //! [`Commands`](crate::system::Commands).
@@ -183,8 +183,10 @@ where
     }
 }
 
-/// A [`Command`] that removes a system previously registered with
-/// [`World::register_system_cached`].
+/// A [`Command`] that removes a system previously registered with one of the following:
+/// - [`Commands::run_system_cached`](crate::system::Commands::run_system_cached)
+/// - [`World::run_system_cached`]
+/// - [`World::register_system_cached`]
 pub fn unregister_system_cached<I, O, M, S>(system: S) -> impl Command<Result>
 where
     I: SystemInput + Send + 'static,

crates/bevy_ecs/src/system/commands/entity_command.rs

@@ -1,5 +1,5 @@
-//! This module contains the definition of the [`EntityCommand`] trait, as well as
-//! blanket implementations of the trait for closures.
+//! Contains the definition of the [`EntityCommand`] trait,
+//! as well as the blanket implementation of the trait for closures.
 //!
 //! It also contains functions that return closures for use with
 //! [`EntityCommands`](crate::system::EntityCommands).
@@ -203,9 +203,10 @@ pub fn retain<T: Bundle>() -> impl EntityCommand {
 ///
 /// # Note
 ///
-/// This will also despawn any [`Children`](crate::hierarchy::Children) entities,
-/// and any other [`RelationshipTarget`](crate::relationship::RelationshipTarget) that is configured to despawn descendants.
-/// This results in "recursive despawn" behavior.
+/// This will also despawn the entities in any [`RelationshipTarget`](crate::relationship::RelationshipTarget)
+/// that is configured to despawn descendants.
+///
+/// For example, this will recursively despawn [`Children`](crate::hierarchy::Children).
 #[track_caller]
 pub fn despawn() -> impl EntityCommand {
     let caller = MaybeLocation::caller();
@@ -227,6 +228,7 @@ pub fn observe<E: Event, B: Bundle, M>(
 }
 
 /// An [`EntityCommand`] that sends a [`Trigger`](crate::observer::Trigger) targeting an entity.
+///
 /// This will run any [`Observer`](crate::observer::Observer) of the given [`Event`] watching the entity.
 #[track_caller]
 pub fn trigger(event: impl Event) -> impl EntityCommand {

crates/bevy_ecs/src/system/commands/parallel_scope.rs

@@ -20,9 +20,13 @@ struct ParallelCommandQueue {
 /// [`Bundle`](crate::prelude::Bundle) type need to be spawned, consider using
 /// [`Commands::spawn_batch`] for better performance.
 ///
-/// Note: Because command application order will depend on how many threads are ran, non-commutative commands may result in non-deterministic results.
+/// # Note
+///
+/// Because command application order will depend on how many threads are ran,
+/// non-commutative commands may result in non-deterministic results.
+///
+/// # Example
 ///
-/// Example:
 /// ```
 /// # use bevy_ecs::prelude::*;
 /// # use bevy_tasks::ComputeTaskPool;