bevy_reflect: Rename UntypedReflectDeserializer to ReflectDeserializer (#12721)

# Objective

We have `ReflectSerializer` and `TypedReflectSerializer`. The former is
the one users will most often use since the latter takes a bit more
effort to deserialize.

However, our deserializers are named `UntypedReflectDeserializer` and
`TypedReflectDeserializer`. There is no obvious indication that
`UntypedReflectDeserializer` must be used with `ReflectSerializer` since
the names don't quite match up.

## Solution

Rename `UntypedReflectDeserializer` back to `ReflectDeserializer`
(initially changed as part of #5723).

Also update the docs for both deserializers (as they were pretty out of
date) and include doc examples.

I also updated the docs for the serializers, too, just so that
everything is consistent.

---

## Changelog

- Renamed `UntypedReflectDeserializer` to `ReflectDeserializer`
- Updated docs for `ReflectDeserializer`, `TypedReflectDeserializer`,
`ReflectSerializer`, and `TypedReflectSerializer`

## Migration Guide

`UntypedReflectDeserializer` has been renamed to `ReflectDeserializer`.
Usages will need to be updated accordingly.

```diff
- let reflect_deserializer = UntypedReflectDeserializer::new(&registry);
+ let reflect_deserializer = ReflectDeserializer::new(&registry);
```

Author: MrGVSV

crates/bevy_reflect/src/lib.rs

@@ -334,7 +334,7 @@
 //! The way it works is by moving the serialization logic into common serializers and deserializers:
 //! * [`ReflectSerializer`]
 //! * [`TypedReflectSerializer`]
-//! * [`UntypedReflectDeserializer`]
+//! * [`ReflectDeserializer`]
 //! * [`TypedReflectDeserializer`]
 //!
 //! All of these structs require a reference to the [registry] so that [type information] can be retrieved,
@@ -347,7 +347,7 @@
 //! and the value is the serialized data.
 //! The `TypedReflectSerializer` will simply output the serialized data.
 //!
-//! The `UntypedReflectDeserializer` can be used to deserialize this map and return a `Box<dyn Reflect>`,
+//! The `ReflectDeserializer` can be used to deserialize this map and return a `Box<dyn Reflect>`,
 //! where the underlying type will be a dynamic type representing some concrete type (except for value types).
 //!
 //! Again, it's important to remember that dynamic types may need to be converted to their concrete counterparts
@@ -357,7 +357,7 @@
 //! ```
 //! # use serde::de::DeserializeSeed;
 //! # use bevy_reflect::{
-//! #     serde::{ReflectSerializer, UntypedReflectDeserializer},
+//! #     serde::{ReflectSerializer, ReflectDeserializer},
 //! #     Reflect, FromReflect, TypeRegistry
 //! # };
 //! #[derive(Reflect, PartialEq, Debug)]
@@ -378,7 +378,7 @@
 //! let serialized_value: String = ron::to_string(&reflect_serializer).unwrap();
 //!
 //! // Deserialize
-//! let reflect_deserializer = UntypedReflectDeserializer::new(&registry);
+//! let reflect_deserializer = ReflectDeserializer::new(&registry);
 //! let deserialized_value: Box<dyn Reflect> = reflect_deserializer.deserialize(
 //!   &mut ron::Deserializer::from_str(&serialized_value).unwrap()
 //! ).unwrap();
@@ -460,7 +460,7 @@
 //! [`serde`]: ::serde
 //! [`ReflectSerializer`]: serde::ReflectSerializer
 //! [`TypedReflectSerializer`]: serde::TypedReflectSerializer
-//! [`UntypedReflectDeserializer`]: serde::UntypedReflectDeserializer
+//! [`ReflectDeserializer`]: serde::ReflectDeserializer
 //! [`TypedReflectDeserializer`]: serde::TypedReflectDeserializer
 //! [registry]: TypeRegistry
 //! [type information]: TypeInfo
@@ -610,7 +610,7 @@ mod tests {
     use super::prelude::*;
     use super::*;
     use crate as bevy_reflect;
-    use crate::serde::{ReflectSerializer, UntypedReflectDeserializer};
+    use crate::serde::{ReflectDeserializer, ReflectSerializer};
     use crate::utility::GenericTypePathCell;
 
     #[test]
@@ -1223,7 +1223,7 @@ mod tests {
         let serialized = to_string_pretty(&serializer, PrettyConfig::default()).unwrap();
 
         let mut deserializer = Deserializer::from_str(&serialized).unwrap();
-        let reflect_deserializer = UntypedReflectDeserializer::new(&registry);
+        let reflect_deserializer = ReflectDeserializer::new(&registry);
         let value = reflect_deserializer.deserialize(&mut deserializer).unwrap();
         let dynamic_struct = value.take::<DynamicStruct>().unwrap();
 
@@ -2383,7 +2383,7 @@ bevy_reflect::tests::Test {
             registry.register::<Quat>();
             registry.register::<f32>();
 
-            let de = UntypedReflectDeserializer::new(&registry);
+            let de = ReflectDeserializer::new(&registry);
 
             let mut deserializer =
                 Deserializer::from_str(data).expect("Failed to acquire deserializer");
@@ -2440,7 +2440,7 @@ bevy_reflect::tests::Test {
             registry.add_registration(Vec3::get_type_registration());
             registry.add_registration(f32::get_type_registration());
 
-            let de = UntypedReflectDeserializer::new(&registry);
+            let de = ReflectDeserializer::new(&registry);
 
             let mut deserializer =
                 Deserializer::from_str(data).expect("Failed to acquire deserializer");