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/array.js

@@ -0,0 +1,70 @@
+const strictEqual = require('assert').strictEqual;
+
+global.TestArrays = class {
+  strings(x) {
+    strictEqual(x, 'y');
+    return 'x';
+  }
+  byteStrings(x) {
+    strictEqual(x, 'yz');
+    return 'xx';
+  }
+  usvStrings(x) {
+    strictEqual(x, 'abc');
+    return 'efg';
+  }
+  f32(x) {
+    strictEqual(x.length, 2);
+    strictEqual(x[0], 1);
+    strictEqual(x[1], 2);
+    return new Float32Array([3, 4, 5]);
+  }
+  f64(x) {
+    strictEqual(x.length, 2);
+    strictEqual(x[0], 1);
+    strictEqual(x[1], 2);
+    return new Float64Array([3, 4, 5]);
+  }
+  i8(x) {
+    strictEqual(x.length, 2);
+    strictEqual(x[0], 1);
+    strictEqual(x[1], 2);
+    return new Int8Array([3, 4, 5]);
+  }
+  i16(x) {
+    strictEqual(x.length, 2);
+    strictEqual(x[0], 1);
+    strictEqual(x[1], 2);
+    return new Int16Array([3, 4, 5]);
+  }
+  i32(x) {
+    strictEqual(x.length, 2);
+    strictEqual(x[0], 1);
+    strictEqual(x[1], 2);
+    return new Int32Array([3, 4, 5]);
+  }
+  u8(x) {
+    strictEqual(x.length, 2);
+    strictEqual(x[0], 1);
+    strictEqual(x[1], 2);
+    return new Uint8Array([3, 4, 5]);
+  }
+  u8Clamped(x) {
+    strictEqual(x.length, 2);
+    strictEqual(x[0], 1);
+    strictEqual(x[1], 2);
+    return new Uint8ClampedArray([3, 4, 5]);
+  }
+  u16(x) {
+    strictEqual(x.length, 2);
+    strictEqual(x[0], 1);
+    strictEqual(x[1], 2);
+    return new Uint16Array([3, 4, 5]);
+  }
+  u32(x) {
+    strictEqual(x.length, 2);
+    strictEqual(x[0], 1);
+    strictEqual(x[1], 2);
+    return new Uint32Array([3, 4, 5]);
+  }
+};