Revert "Botched the math last time... Fix that and add tests to make sure it works."

Since it contains breaking change to plotters-backend, revert at this
time and move the commit to the next release branch

This reverts commit 715dd7a.

Author: 38

plotters-backend/src/text.rs

@@ -151,12 +151,10 @@ impl FontTransform {
             FontTransform::Rotate90 => (-y, x),
             FontTransform::Rotate180 => (-x, -y),
             FontTransform::Rotate270 => (y, -x),
-            FontTransform::RotateAngle(angle) => {
-                let (x, y) = (x as f32, y as f32);
-                let (sin, cos) = angle.to_radians().sin_cos();
-                let (x, y) = (x * cos - y * sin, x * sin + y * cos);
-                (x.round() as i32, y.round() as i32)
-            }
+            FontTransform::RotateAngle(angle) => (
+                ((x as f32) * angle.cos()).round() as i32,
+                ((y as f32) * angle.sin()).round() as i32,
+            ),
         }
     }
 }
@@ -251,19 +249,3 @@ pub trait BackendTextStyle {
         draw: DrawFunc,
     ) -> Result<Result<(), E>, Self::FontError>;
 }
-
-#[cfg(test)]
-mod tests {
-    use crate::FontTransform;
-
-    #[test]
-    fn text_rotation_works() {
-        assert_eq!(FontTransform::None.transform(1, 0), (1, 0));
-        assert_eq!(FontTransform::Rotate90.transform(1, 0), (0, 1));
-        assert_eq!(FontTransform::Rotate180.transform(1, 0), (-1, 0));
-        assert_eq!(FontTransform::Rotate270.transform(1, 0), (0, -1));
-
-        assert_eq!(FontTransform::RotateAngle(45f32).transform(10, 0), (7, 7));
-        assert_eq!(FontTransform::RotateAngle(45f32).transform(0, 10), (-7, 7));
-    }
-}