Make AssetMetaCheck a field on the asset plugin (#13177)

# Objective

There's a TODO comment above the `AssetMetaCheck` enum mentioning this
should have been done in 0.13

## Solution

Do it in 0.14

## Testing

I've checked that all the asset tests compile. I've also run the
asset_processing and asset_settings tests and they both work.

---

## Changelog

### Changed
-
[`AssetMetaCheck`](https://docs.rs/bevy/latest/bevy/asset/enum.AssetMetaCheck.html)
is no longer a resource and is now a field on the
[`AssetPlugin`](https://docs.rs/bevy/latest/bevy/asset/struct.AssetPlugin.html).

## Migration Guide

Changes to how bevy handles asset meta files now need to be specified
when inserting the `AssetPlugin`.

crates/bevy_asset/src/lib.rs

@@ -55,7 +55,6 @@ use bevy_app::{App, Last, Plugin, PreUpdate};
 use bevy_ecs::{
     reflect::AppTypeRegistry,
     schedule::{IntoSystemConfigs, IntoSystemSetConfigs, SystemSet},
-    system::Resource,
     world::FromWorld,
 };
 use bevy_reflect::{FromReflect, GetTypeRegistration, Reflect, TypePath};
@@ -90,6 +89,8 @@ pub struct AssetPlugin {
     pub watch_for_changes_override: Option<bool>,
     /// The [`AssetMode`] to use for this server.
     pub mode: AssetMode,
+    /// How/If asset meta files should be checked.
+    pub meta_check: AssetMetaCheck,
 }
 
 #[derive(Debug)]
@@ -118,8 +119,7 @@ pub enum AssetMode {
 
 /// Configures how / if meta files will be checked. If an asset's meta file is not checked, the default meta for the asset
 /// will be used.
-// TODO: To avoid breaking Bevy 0.12 users in 0.12.1, this is a Resource. In Bevy 0.13 this should be changed to a field on AssetPlugin (if it is still needed).
+#[derive(Debug, Default, Clone)]
-#[derive(Debug, Default, Clone, Resource)]
 pub enum AssetMetaCheck {
     /// Always check if assets have meta files. If the meta does not exist, the default meta will be used.
     #[default]
@@ -137,6 +137,7 @@ impl Default for AssetPlugin {
             file_path: Self::DEFAULT_UNPROCESSED_FILE_PATH.to_string(),
             processed_file_path: Self::DEFAULT_PROCESSED_FILE_PATH.to_string(),
             watch_for_changes_override: None,
+            meta_check: AssetMetaCheck::default(),
         }
     }
 }
@@ -171,16 +172,11 @@ impl Plugin for AssetPlugin {
                 AssetMode::Unprocessed => {
                     let mut builders = app.world_mut().resource_mut::<AssetSourceBuilders>();
                     let sources = builders.build_sources(watch, false);
-                    let meta_check = app
-                        .world()
-                        .get_resource::<AssetMetaCheck>()
-                        .cloned()
-                        .unwrap_or_else(AssetMetaCheck::default);
 
                     app.insert_resource(AssetServer::new_with_meta_check(
                         sources,
                         AssetServerMode::Unprocessed,
-                        meta_check,
+                        self.meta_check.clone(),
                         watch,
                     ));
                 }