Migrate webidl tests to wasm_bindgen_test (#590)

This commit moves the `webidl/tests` folder to a new `crates/webidl-tests` crate
(to have a test-only build script) and ports them to the `#[wasm_bindgen_test]`
attribute, which should hopefully make testing much speedier for execution!

crates/webidl-tests/simple.rs

@@ -0,0 +1,81 @@
+use wasm_bindgen_test::*;
+
+include!(concat!(env!("OUT_DIR"), "/simple.rs"));
+
+#[wasm_bindgen_test]
+fn method() {
+    let pi = Method::new(3.14159).unwrap();
+    let e = Method::new(2.71828).unwrap();
+    assert!(pi.my_cmp(&pi));
+    assert!(!pi.my_cmp(&e));
+    assert!(!e.my_cmp(&pi));
+    assert!(e.my_cmp(&e));
+}
+
+#[wasm_bindgen_test]
+fn property() {
+    let x = Property::new(3.14159).unwrap();
+    assert_eq!(x.value(), 3.14159);
+    assert_ne!(x.value(), 2.71828);
+    x.set_value(2.71828);
+    assert_ne!(x.value(), 3.14159);
+    assert_eq!(x.value(), 2.71828);
+}
+
+#[wasm_bindgen_test]
+fn named_constructor() {
+    let x = NamedConstructor::new(3.14159).unwrap();
+    assert_eq!(x.value(), 3.14159);
+    assert_ne!(x.value(), 0.);
+}
+
+#[wasm_bindgen_test]
+fn static_method() {
+    assert_eq!(StaticMethod::swap(3.14159), 0.);
+    assert_eq!(StaticMethod::swap(2.71828), 3.14159);
+    assert_ne!(StaticMethod::swap(2.71828), 3.14159);
+    assert_eq!(StaticMethod::swap(3.14159), 2.71828);
+    assert_ne!(StaticMethod::swap(3.14159), 2.71828);
+}
+
+#[wasm_bindgen_test]
+fn static_property() {
+    assert_eq!(StaticProperty::value(), 0.);
+    StaticProperty::set_value(3.14159);
+    assert_eq!(StaticProperty::value(), 3.14159);
+    assert_ne!(StaticProperty::value(), 2.71828);
+    StaticProperty::set_value(2.71828);
+    assert_eq!(StaticProperty::value(), 2.71828);
+    assert_ne!(StaticProperty::value(), 3.14159);
+}
+
+#[wasm_bindgen_test]
+fn one_method_using_an_undefined_import_doesnt_break_all_other_methods() {
+    let f = UndefinedMethod::new().unwrap();
+    assert!(f.ok_method());
+}
+
+#[wasm_bindgen_test]
+fn unforgeable_is_structural() {
+    let f = Unforgeable::new().unwrap();
+    assert_eq!(f.uno(), 1);
+    assert_eq!(f.dos(), 2);
+}
+
+#[wasm_bindgen_test]
+fn partial_interface() {
+    let f = PartialInterface::new().unwrap();
+    assert_eq!(f.un(), 1);
+    assert_eq!(f.deux(), 2);
+    assert_eq!(f.trois(), 3);
+    assert_eq!(f.quatre(), 4);
+}
+
+#[wasm_bindgen_test]
+fn mixin() {
+    let f = MixinFoo::new(1).unwrap();
+    assert_eq!(f.bar(), 1);
+    MixinFoo::set_default_bar(7);
+    f.add_to_bar(MixinFoo::default_bar());
+    assert_eq!(f.bar(), 8);
+}