servo: Merge #19282 - Use macro to impl From for font variant (from CYBAI:use-macro-for-font-variant); r=canaltinova

As I discussed in #19277, I'd like to change the implementation for `From` of font variant to use macro, `impl_gecko_keyword_conversions`.
r? @emilio

---
- [x] `./mach build -d` does not report any errors
- [x] `./mach test-tidy` does not report any errors
- [x] These changes update `From` impl for font variant to use macro `impl_gecko_keyword_conversions`.
- [x] These changes do not require tests

Source-Repo: https://github.com/servo/servo
Source-Revision: 63bd783c55ab0c0f9abb1a8fa07f20932c77b764

--HG--
extra : subtree_source : https%3A//hg.mozilla.org/projects/converted-servo-linear
extra : subtree_revision : 3b84f9e94c75f791a42835a47e0beb989f628bcf

servo/components/style/values/specified/font.rs

@@ -929,18 +929,7 @@ impl ToCss for VariantEastAsian {
 }
 
 #[cfg(feature = "gecko")]
-impl From<u16> for VariantEastAsian {
-    fn from(bits: u16) -> VariantEastAsian {
-        VariantEastAsian::from_gecko_keyword(bits)
-    }
-}
-
-#[cfg(feature = "gecko")]
-impl From<VariantEastAsian> for u16 {
-    fn from(v: VariantEastAsian) -> u16 {
-        v.to_gecko_keyword()
-    }
-}
+impl_gecko_keyword_conversions!(VariantEastAsian, u16);
 
 /// Asserts that all variant-east-asian matches its NS_FONT_VARIANT_EAST_ASIAN_* value.
 #[cfg(feature = "gecko")]
@@ -1176,18 +1165,7 @@ impl ToCss for VariantLigatures {
 }
 
 #[cfg(feature = "gecko")]
-impl From<u16> for VariantLigatures {
-    fn from(bits: u16) -> VariantLigatures {
-        VariantLigatures::from_gecko_keyword(bits)
-    }
-}
-
-#[cfg(feature = "gecko")]
-impl From<VariantLigatures> for u16 {
-    fn from(v: VariantLigatures) -> u16 {
-        v.to_gecko_keyword()
-    }
-}
+impl_gecko_keyword_conversions!(VariantLigatures, u16);
 
 /// Asserts that all variant-east-asian matches its NS_FONT_VARIANT_EAST_ASIAN_* value.
 #[cfg(feature = "gecko")]