Auto merge of #14703 - canaltinova:perspective-transform, r=Wafflespeanut

Add gecko glue for perspective/transform properties

<!-- Please describe your changes on the following line: -->
To be able to add glue for these properties,  we needed to change their structs. They are moved from effects to box and added stylo glue.
This PR covers these properties:
- perspective
- perspective-origin
- backface-visibility
- transform-box
- transform-style
- transform-origin

---
<!-- Thank you for contributing to Servo! Please replace each `[ ]` by `[X]` when the step is complete, and replace `__` with appropriate data: -->
- [X] `./mach build -d` does not report any errors
- [X] `./mach test-tidy` does not report any errors

<!-- Either: -->
- [X] These changes do not require tests because they are stylo changes

<!-- Pull requests that do not address these steps are welcome, but they will require additional verification as part of the review process. -->

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components/style/gecko/values.rs

@@ -9,7 +9,7 @@ use cssparser::RGBA;
 use gecko_bindings::structs::{nsStyleCoord, StyleShapeRadius};
 use gecko_bindings::sugar::ns_style_coord::{CoordData, CoordDataMut, CoordDataValue};
 use std::cmp::max;
-use values::{Auto, Either};
+use values::{Auto, Either, None_};
 use values::computed::{Angle, LengthOrPercentageOrNone, Number};
 use values::computed::{LengthOrPercentage, LengthOrPercentageOrAuto};
 use values::computed::basic_shape::ShapeRadius;
@@ -207,6 +207,20 @@ impl GeckoStyleCoordConvertible for Auto {
     }
 }
 
+impl GeckoStyleCoordConvertible for None_ {
+    fn to_gecko_style_coord<T: CoordDataMut>(&self, coord: &mut T) {
+        coord.set_value(CoordDataValue::None)
+    }
+
+    fn from_gecko_style_coord<T: CoordData>(coord: &T) -> Option<Self> {
+        if let CoordDataValue::None = coord.as_value() {
+            Some(None_)
+        } else {
+            None
+        }
+    }
+}
+
 pub fn convert_rgba_to_nscolor(rgba: &RGBA) -> u32 {
     (((rgba.alpha * 255.0).round() as u32) << 24) |
     (((rgba.blue  * 255.0).round() as u32) << 16) |