Auto merge of #18068 - BorisChiou:stylo/animation/perspective, r=birtles

Fix the conversion from Perspective into ComputedMatrix.

We convert a perspective function into a ComputedMatrix, but we apply the
perspective length to a wrong matrix item. We should put it into m34,
instead of m43. m43 is for translate parameter Z.

---
- [X] `./mach build -d` does not report any errors
- [X] `./mach test-tidy` does not report any errors
- [X] These changes fix [Bug 1389023](https://bugzilla.mozilla.org/show_bug.cgi?id=1389023).
- [X] These changes do not require tests because we have many transform tests in Gecko already. However, those tests may not be enough, so we should add more in Gecko later.

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components/style/properties/helpers/animated_properties.mako.rs

@@ -1474,11 +1474,17 @@ fn add_weighted_transform_lists(from_list: &[TransformOperation],
                     }
                 }
                 (&TransformOperation::Perspective(fd),
-                 &TransformOperation::Perspective(_td)) => {
+                 &TransformOperation::Perspective(td)) => {
                     let mut fd_matrix = ComputedMatrix::identity();
                     let mut td_matrix = ComputedMatrix::identity();
-                    fd_matrix.m43 = -1. / fd.to_f32_px();
+                    if fd.0 > 0 {
-                    td_matrix.m43 = -1. / _td.to_f32_px();
+                        fd_matrix.m34 = -1. / fd.to_f32_px();
+                    }
+
+                    if td.0 > 0 {
+                        td_matrix.m34 = -1. / td.to_f32_px();
+                    }
+
                     let sum = fd_matrix.add_weighted(&td_matrix, self_portion, other_portion)
                                        .unwrap();
                     result.push(TransformOperation::Matrix(sum));