Auto merge of #13386 - Manishearth:style-testing, r=emilio

Run style tests with all properties included

This turns on all properties (including stylo-only ones) when the style unit tests are compiled. This lets us test the parsing of gecko-only properties.

These tests can't go in tests/stylo since this introduces dependencies on `Gecko_*` symbols. This method lets us test parsing and serialization of geckolib properties compiled in Servo mode (e.g. using Servo atoms, Servo URLs)

r? @emilio

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tests/unit/style/properties/scaffolding.rs

@@ -21,6 +21,7 @@ fn properties_list_json() {
         .arg(&script)
         .arg("servo")
         .arg("html")
+        .arg("regular")
         .status()
         .unwrap();
     assert!(status.success());