Support tuple structs in AnimatedField (#16747)

# Objective

Partially fixes #16736.

## Solution

`AnimatedField::new_unchecked` now supports tuple struct fields.
`animated_field!` is unchanged.

## Testing

Added a test to make sure common and simple uses of
`AnimatedField::new_unchecked` with tuple structs don't panic.

---------

Co-authored-by: yonzebu <[email protected]>

crates/bevy_animation/src/animation_curves.rs

@@ -243,18 +243,26 @@ where
 
 impl<C: Typed, P, F: Fn(&mut C) -> &mut P + 'static> AnimatedField<C, P, F> {
     /// Creates a new instance of [`AnimatedField`]. This operates under the assumption that
-    /// `C` is a reflect-able struct with named fields, and that `field_name` is a valid field on that struct.
+    /// `C` is a reflect-able struct, and that `field_name` is a valid field on that struct.
     ///
     /// # Panics
-    /// If the type of `C` is not a struct with named fields or if the `field_name` does not exist.
+    /// If the type of `C` is not a struct or if the `field_name` does not exist.
     pub fn new_unchecked(field_name: &str, func: F) -> Self {
-        let TypeInfo::Struct(struct_info) = C::type_info() else {
+        let field_index;
+        if let TypeInfo::Struct(struct_info) = C::type_info() {
+            field_index = struct_info
+                .index_of(field_name)
+                .expect("Field name should exist");
+        } else if let TypeInfo::TupleStruct(struct_info) = C::type_info() {
+            field_index = field_name
+                .parse()
+                .expect("Field name should be a valid tuple index");
+            if field_index >= struct_info.field_len() {
+                panic!("Field name should be a valid tuple index");
+            }
+        } else {
             panic!("Only structs are supported in `AnimatedField::new_unchecked`")
-        };
-
-        let field_index = struct_info
-            .index_of(field_name)
-            .expect("Field name should exist");
+        }
 
         Self {
             func,
@@ -984,3 +992,21 @@ macro_rules! animated_field {
         })
     };
 }
+
+#[cfg(test)]
+mod tests {
+    use super::*;
+
+    #[test]
+    fn test_animated_field_tuple_struct_simple_uses() {
+        #[derive(Clone, Debug, Component, Reflect)]
+        struct A(f32);
+        let _ = AnimatedField::new_unchecked("0", |a: &mut A| &mut a.0);
+
+        #[derive(Clone, Debug, Component, Reflect)]
+        struct B(f32, f64, f32);
+        let _ = AnimatedField::new_unchecked("0", |b: &mut B| &mut b.0);
+        let _ = AnimatedField::new_unchecked("1", |b: &mut B| &mut b.1);
+        let _ = AnimatedField::new_unchecked("2", |b: &mut B| &mut b.2);
+    }
+}