Remove From implementations from the direction types (#10857)

This removes the `From<Vec2/3>` implementations for the direction types.
It doesn't seem right to have when it only works if the vector is
nonzero and finite and produces NaN otherwise.

Added `Direction2d/3d::new` which uses `Vec2/3::try_normalize` to
guarantee it returns either a valid direction or `None`.

This should make it impossible to create an invalid direction, which I
think was the intention with these types.

crates/bevy_math/src/primitives/dim2.rs

@@ -5,13 +5,14 @@ use crate::Vec2;
 #[derive(Clone, Copy, Debug)]
 pub struct Direction2d(Vec2);
 
-impl From<Vec2> for Direction2d {
-    fn from(value: Vec2) -> Self {
-        Self(value.normalize())
-    }
-}
-
 impl Direction2d {
+    /// Create a direction from a finite, nonzero [`Vec2`].
+    ///
+    /// Returns `None` if the input is zero (or very close to zero), or non-finite.
+    pub fn new(value: Vec2) -> Option<Self> {
+        value.try_normalize().map(Self)
+    }
+
     /// Create a direction from a [`Vec2`] that is already normalized
     pub fn from_normalized(value: Vec2) -> Self {
         debug_assert!(value.is_normalized());

crates/bevy_math/src/primitives/dim3.rs

@@ -5,13 +5,14 @@ use crate::Vec3;
 #[derive(Clone, Copy, Debug)]
 pub struct Direction3d(Vec3);
 
-impl From<Vec3> for Direction3d {
-    fn from(value: Vec3) -> Self {
-        Self(value.normalize())
-    }
-}
-
 impl Direction3d {
+    /// Create a direction from a finite, nonzero [`Vec3`].
+    ///
+    /// Returns `None` if the input is zero (or very close to zero), or non-finite.
+    pub fn new(value: Vec3) -> Option<Self> {
+        value.try_normalize().map(Self)
+    }
+
     /// Create a direction from a [`Vec3`] that is already normalized
     pub fn from_normalized(value: Vec3) -> Self {
         debug_assert!(value.is_normalized());