style: Support unprefixed min-content and max-content.

Support unprefixed min-content and max-content and treat the prefixed
version as aliases for
1. width, min-width, max-width if inline-axis is horizontal, and
2. height, min-height, max-height if inline-axis is vertical, and
3. inline-size, min-inline-size, max-inline-size, and
4. flex-basis.

Besides, update the test cases to use unprefixed max-content and
min-content.

Differential Revision: https://phabricator.services.mozilla.com/D7536

components/style/values/computed/length.rs

@@ -985,8 +985,10 @@ pub type NonNegativeLengthOrPercentageOrNormal = Either<NonNegativeLengthOrPerce
 )]
 #[repr(u8)]
 pub enum ExtremumLength {
-    MozMaxContent,
+    #[parse(aliases = "-moz-max-content")]
-    MozMinContent,
+    MaxContent,
+    #[parse(aliases = "-moz-min-content")]
+    MinContent,
     MozFitContent,
     MozAvailable,
 }