Add synonyms for transform relative vectors (bevyengine#1667)

Fixes bevyengine#1663.

I think the directions are correct (same as [here](https://docs.godotengine.org/en/stable/classes/class_vector3.html?highlight=forward#constants)), but please double check because I might have mixed them up.

Co-authored-by: guimcaballero <guim.caballero@gmail.com>
Co-authored-by: Guim Caballero <guim.caballero@gmail.com>

crates/bevy_transform/src/components/global_transform.rs

@@ -118,18 +118,54 @@ impl GlobalTransform {
         self.rotation * Vec3::X
     }
 
+    /// Equivalent to -local_x()
+    #[inline]
+    pub fn left(&self) -> Vec3 {
+        -self.local_x()
+    }
+
+    /// Equivalent to local_x()
+    #[inline]
+    pub fn right(&self) -> Vec3 {
+        self.local_x()
+    }
+
     /// Get the unit vector in the local y direction
     #[inline]
     pub fn local_y(&self) -> Vec3 {
         self.rotation * Vec3::Y
     }
 
+    /// Equivalent to local_y()
+    #[inline]
+    pub fn up(&self) -> Vec3 {
+        self.local_y()
+    }
+
+    /// Equivalent to -local_y()
+    #[inline]
+    pub fn down(&self) -> Vec3 {
+        -self.local_y()
+    }
+
     /// Get the unit vector in the local z direction
     #[inline]
     pub fn local_z(&self) -> Vec3 {
         self.rotation * Vec3::Z
     }
 
+    /// Equivalent to -local_z()
+    #[inline]
+    pub fn forward(&self) -> Vec3 {
+        -self.local_z()
+    }
+
+    /// Equivalent to local_z()
+    #[inline]
+    pub fn back(&self) -> Vec3 {
+        self.local_z()
+    }
+
     #[doc(hidden)]
     #[inline]
     pub fn rotate(&mut self, rotation: Quat) {

crates/bevy_transform/src/components/transform.rs

@@ -130,18 +130,54 @@ impl Transform {
         self.rotation * Vec3::X
     }
 
+    /// Equivalent to -local_x()
+    #[inline]
+    pub fn left(&self) -> Vec3 {
+        -self.local_x()
+    }
+
+    /// Equivalent to local_x()
+    #[inline]
+    pub fn right(&self) -> Vec3 {
+        self.local_x()
+    }
+
     /// Get the unit vector in the local y direction.
     #[inline]
     pub fn local_y(&self) -> Vec3 {
         self.rotation * Vec3::Y
     }
 
+    /// Equivalent to local_y()
+    #[inline]
+    pub fn up(&self) -> Vec3 {
+        self.local_y()
+    }
+
+    /// Equivalent to -local_y()
+    #[inline]
+    pub fn down(&self) -> Vec3 {
+        -self.local_y()
+    }
+
     /// Get the unit vector in the local z direction.
     #[inline]
     pub fn local_z(&self) -> Vec3 {
         self.rotation * Vec3::Z
     }
 
+    /// Equivalent to -local_z()
+    #[inline]
+    pub fn forward(&self) -> Vec3 {
+        -self.local_z()
+    }
+
+    /// Equivalent to local_z()
+    #[inline]
+    pub fn back(&self) -> Vec3 {
+        self.local_z()
+    }
+
     /// Rotates the transform by the given rotation.
     #[inline]
     pub fn rotate(&mut self, rotation: Quat) {