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.js

@@ -0,0 +1,110 @@
+global.Method = class Method {
+  constructor(value) {
+    this.value = value;
+  }
+  myCmp(other) {
+    return this.value === other.value;
+  }
+};
+
+global.Property = class Property {
+  constructor(value) {
+    this._value = value;
+  }
+
+  get value() {
+    return this._value;
+  }
+
+  set value(value) {
+    this._value = value;
+  }
+};
+
+global.NamedConstructor = class NamedConstructor {
+  constructor() {
+    this._value = 0;
+  }
+
+  get value(){
+    return this._value;
+  }
+};
+
+global.NamedConstructorBar = class NamedConstructorBar extends NamedConstructor {
+  constructor(_value) {
+    super();
+    this._value = _value;
+  }
+};
+
+global.StaticMethod = class StaticMethod {
+  static swap(value) {
+    const res = StaticMethod.value;
+    StaticMethod.value = value;
+    return res;
+  }
+};
+
+StaticMethod.value = 0;
+
+global.StaticProperty = class StaticProperty {
+  static get value(){
+    return StaticProperty._value;
+  }
+
+  static set value(value) {
+    StaticProperty._value = value;
+  }
+};
+
+StaticProperty._value = 0;
+
+global.UndefinedMethod = class UndefinedMethod {
+  constructor() {}
+  ok_method() {
+    return true;
+  }
+};
+
+global.Unforgeable = class Unforgeable {
+  constructor() {
+    this.uno = 1;
+  }
+  get dos() {
+    return 2;
+  }
+};
+
+global.PartialInterface = class PartialInterface {
+  get un() {
+    return 1;
+  }
+  deux() {
+    return 2;
+  }
+  get trois() {
+    return 3;
+  }
+  quatre() {
+    return 4;
+  }
+};
+
+global.MixinFoo = class MixinFoo {
+  constructor(bar) {
+    this._bar = bar | MixinFoo.defaultBar;
+  }
+  static get defaultBar() {
+    return MixinFoo._defaultBar;
+  }
+  static set defaultBar(defaultBar) {
+    MixinFoo._defaultBar = defaultBar;
+  }
+  get bar() {
+    return this._bar;
+  }
+  addToBar(other) {
+    this._bar += other;
+  }
+};