Collection of helper constants and functions for testing RABs (#4030)

Collection of helper constants and functions for testing resizable array buffers.

These are the parts of the code in RAB staging tests that are heavily repeated.
In order to somewhat compact the migration of RAB staging tests (see PR #3888).

harness/resizableArrayBufferUtils.js

@@ -0,0 +1,151 @@
+// Copyright 2023 the V8 project authors. All rights reserved.
+// This code is governed by the BSD license found in the LICENSE file.
+
+/*---
+description: |
+    Collection of helper constants and functions for testing resizable array buffers.
+defines:
+  - floatCtors
+  - ctors
+  - MyBigInt64Array
+  - CreateResizableArrayBuffer
+  - WriteToTypedArray
+  - Convert
+  - ToNumbers
+  - CreateRabForTest
+  - CollectValuesAndResize
+  - TestIterationAndResize
+features: [BigInt]
+---*/
+
+class MyUint8Array extends Uint8Array {
+}
+
+class MyFloat32Array extends Float32Array {
+}
+
+class MyBigInt64Array extends BigInt64Array {
+}
+
+const builtinCtors = [
+  Uint8Array,
+  Int8Array,
+  Uint16Array,
+  Int16Array,
+  Uint32Array,
+  Int32Array,
+  Float32Array,
+  Float64Array,
+  Uint8ClampedArray,
+];
+
+// BigInt and Float16Array are newer features adding them above unconditionally
+// would cause implementations lacking it to fail every test which uses it.
+if (typeof Float16Array !== 'undefined') {
+  builtinCtors.push(Float16Array);
+}
+
+if (typeof BigInt !== 'undefined') {
+    builtinCtors.push(BigUint64Array);
+    builtinCtors.push(BigInt64Array);
+}
+
+const floatCtors = [
+  Float32Array,
+  Float64Array,
+  MyFloat32Array
+];
+
+if (typeof Float16Array !== 'undefined') {
+  floatCtors.push(Float16Array);
+}
+
+const ctors = [
+  ...builtinCtors,
+  MyUint8Array,
+  MyFloat32Array
+];
+
+if (typeof BigInt !== 'undefined') {
+    ctors.push(MyBigInt64Array);
+}
+
+function CreateResizableArrayBuffer(byteLength, maxByteLength) {
+  return new ArrayBuffer(byteLength, { maxByteLength: maxByteLength });
+}
+
+function WriteToTypedArray(array, index, value) {
+  if (array instanceof BigInt64Array || array instanceof BigUint64Array) {
+    array[index] = BigInt(value);
+  } else {
+    array[index] = value;
+  }
+}
+
+function Convert(item) {
+  if (typeof item == 'bigint') {
+    return Number(item);
+  }
+  return item;
+}
+
+function ToNumbers(array) {
+  let result = [];
+  for (let i = 0; i < array.length; i++) {
+    let item = array[i];
+    result.push(Convert(item));
+  }
+  return result;
+}
+
+function CreateRabForTest(ctor) {
+  const rab = CreateResizableArrayBuffer(4 * ctor.BYTES_PER_ELEMENT, 8 * ctor.BYTES_PER_ELEMENT);
+  // Write some data into the array.
+  const taWrite = new ctor(rab);
+  for (let i = 0; i < 4; ++i) {
+    WriteToTypedArray(taWrite, i, 2 * i);
+  }
+  return rab;
+}
+
+function CollectValuesAndResize(n, values, rab, resizeAfter, resizeTo) {
+  if (typeof n == 'bigint') {
+    values.push(Number(n));
+  } else {
+    values.push(n);
+  }
+  if (values.length == resizeAfter) {
+    rab.resize(resizeTo);
+  }
+  return true;
+}
+
+function TestIterationAndResize(iterable, expected, rab, resizeAfter, newByteLength) {
+  let values = [];
+  let resized = false;
+  var arrayValues = false;
+
+  for (const value of iterable) {
+    if (Array.isArray(value)) {
+      arrayValues = true;
+      values.push([
+        value[0],
+        Number(value[1])
+      ]);
+    } else {
+      values.push(Number(value));
+    }
+    if (!resized && values.length == resizeAfter) {
+      rab.resize(newByteLength);
+      resized = true;
+    }
+  }
+  if (!arrayValues) {
+      assert.compareArray([].concat(values), expected, "TestIterationAndResize: list of iterated values");
+  } else {
+    for (let i = 0; i < expected.length; i++) {
+      assert.compareArray(values[i], expected[i], "TestIterationAndResize: list of iterated lists of values");
+    }
+  }
+  assert(resized, "TestIterationAndResize: resize condition should have been hit");
+}