Auto merge of #14394 - jcdyer:jcdyer/either-column-width, r=Wafflespeanut

Convert column-width to use Either

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* Converted column-width to use `Either<Length, Auto>`
* Added gecko glue code
* Cleaned up old column-width glue code

---
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- [x] `./mach build -d` does not report any errors
- [x] `./mach test-tidy` does not report any errors
- [x] These changes fix #14350 (github issue number if applicable).

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- [ ] There are tests for these changes OR
- [x] These changes do not require tests because tests already surround the refactored code.
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components/style/gecko/values.rs

@@ -10,7 +10,7 @@ use gecko_bindings::structs::{NS_RADIUS_CLOSEST_SIDE, NS_RADIUS_FARTHEST_SIDE};
 use gecko_bindings::structs::nsStyleCoord;
 use gecko_bindings::sugar::ns_style_coord::{CoordData, CoordDataMut, CoordDataValue};
 use std::cmp::max;
-use values::Either;
+use values::{Auto, Either};
 use values::computed::{Angle, LengthOrPercentageOrNone, Number};
 use values::computed::{LengthOrPercentage, LengthOrPercentageOrAuto};
 use values::computed::basic_shape::ShapeRadius;
@@ -187,6 +187,20 @@ impl GeckoStyleCoordConvertible for Angle {
     }
 }
 
+impl GeckoStyleCoordConvertible for Auto {
+    fn to_gecko_style_coord<T: CoordDataMut>(&self, coord: &mut T) {
+        coord.set_value(CoordDataValue::Auto)
+    }
+
+    fn from_gecko_style_coord<T: CoordData>(coord: &T) -> Option<Self> {
+        if let CoordDataValue::Auto = coord.as_value() {
+            Some(Auto)
+        } 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) |