Auto merge of #17973 - ferjm:ordered-map, r=heycam

stylo: ensure consistent order for custom properties computed values

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

From https://bugzilla.mozilla.org/show_bug.cgi?id=1379577

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components/style/properties/properties.mako.rs

@@ -2314,7 +2314,7 @@ impl ComputedValuesInner {
             PropertyDeclarationId::Custom(name) => {
                 self.custom_properties
                     .as_ref()
-                    .and_then(|map| map.get_computed_value(name))
+                    .and_then(|map| map.get(name))
                     .map(|value| value.to_css_string())
                     .unwrap_or(String::new())
             }