Add missing closing ticks for inline examples and some cleanup (#3573)

# Objective

- clean up documentation and inline examples

## Solution

- add missing closing "```"
- remove stray "```"
- remove whitespace in inline examples
- unify inline examples (remove some `rust` labels)

crates/bevy_dylib/src/lib.rs

@@ -36,7 +36,7 @@
 //! Manually enabling dynamic linking is achieved by adding `bevy_dylib` as a dependency and
 //! adding the following code to the `main.rs` file:
 //!
-//! ```rust
+//! ```
 //! #[allow(unused_imports)]
 //! use bevy_dylib;
 //! ```
@@ -44,7 +44,7 @@
 //! It is recommended to disable the `bevy_dylib` dependency in release mode by adding the
 //! following code to the `use` statement to avoid having to ship additional files with your game:
 //!
-//! ```rust
+//! ```
 //! #[allow(unused_imports)]
 //! #[cfg(debug_assertions)] // new
 //! use bevy_dylib;

crates/bevy_ecs/src/schedule/mod.rs

@@ -161,6 +161,7 @@ impl Schedule {
     /// # schedule.add_stage("target_stage", SystemStage::parallel());
     /// #
     /// schedule.add_stage_before("target_stage", "my_stage", SystemStage::parallel());
+    /// ```
     pub fn add_stage_before<S: Stage>(
         &mut self,
         target: impl StageLabel,
@@ -197,6 +198,7 @@ impl Schedule {
     /// # schedule.add_stage("my_stage", SystemStage::parallel());
     /// #
     /// schedule.add_system_to_stage("my_stage", my_system);
+    /// ```
     pub fn add_system_to_stage<Params>(
         &mut self,
         stage_label: impl StageLabel,
@@ -324,6 +326,7 @@ impl Schedule {
     /// # schedule.add_stage("my_stage", SystemStage::parallel());
     /// #
     /// let stage = schedule.get_stage_mut::<SystemStage>(&"my_stage").unwrap();
+    /// ```
     pub fn get_stage_mut<T: Stage>(&mut self, label: &dyn StageLabel) -> Option<&mut T> {
         self.stages
             .get_mut(label)

crates/bevy_render/src/mesh/mesh/conversions.rs

@@ -3,7 +3,7 @@
 //!
 //! # Examples
 //!
-//! ```rust
+//! ```
 //! use bevy_render::mesh::VertexAttributeValues;
 //!
 //! // creating std::vec::Vec

examples/ecs/system_sets.rs

@@ -46,7 +46,6 @@ pub enum PhysicsSystem {
 /// ordering can then change between invocations.
 ///
 /// Lastly a system with run criterion _done_ is used to exit the app.
-/// ```
 fn main() {
     App::new()
         .add_plugins(DefaultPlugins)

src/lib.rs

@@ -24,7 +24,7 @@
 //!    println!("hello world");
 //! }
 //! ```
-
+//!
 //! Don't let the simplicity of the example above fool you. Bevy is a [fully featured game engine](https://bevyengine.org)
 //! and it gets more powerful every day!
 //!