Auto merge of #18396 - jdm:codesize, r=emilio

Reduce duplication in generated ServoComputedData::to_declaration_block.

This reduces the size of the code in libXUL by 23.4k according to bloaty.

---
- [x] `./mach build -d` does not report any errors
- [x] `./mach test-tidy` does not report any errors

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components/style/properties/gecko.mako.rs

@@ -342,11 +342,10 @@ impl ComputedValuesInner {
     pub fn is_multicol(&self) -> bool { false }
 
     pub fn to_declaration_block(&self, property: PropertyDeclarationId) -> PropertyDeclarationBlock {
-        match property {
+        let value = match property {
             % for prop in data.longhands:
                 % if prop.animatable:
                     PropertyDeclarationId::Longhand(LonghandId::${prop.camel_case}) => {
-                         PropertyDeclarationBlock::with_one(
                         PropertyDeclaration::${prop.camel_case}(
                             % if prop.boxed:
                                 Box::new(
@@ -356,15 +355,14 @@ impl ComputedValuesInner {
                             % if prop.boxed:
                                 )
                             % endif
-                            ),
-                            Importance::Normal
                         )
                     },
                 % endif
             % endfor
             PropertyDeclarationId::Custom(_name) => unimplemented!(),
             _ => unimplemented!()
-        }
+        };
+        PropertyDeclarationBlock::with_one(value, Importance::Normal)
     }
 }