Add CatmullRomCurve and CatmullRomSpline (#47547)

This adds CatmullRomCurve animation curve, and a CatmullRomSpline, which is what it uses to do interpolation.

This allows us to create animation curves which can smoothly interpolate the values given to the curve.

Since I've introduced a 2D spline curve, I also created a Curve2D base class for such parametric curves.

dev/benchmarks/microbenchmarks/lib/geometry/curves_bench.dart

@@ -0,0 +1,60 @@
+// Copyright 2014 The Flutter Authors. All rights reserved.
+// Use of this source code is governed by a BSD-style license that can be
+// found in the LICENSE file.
+
+import 'dart:ui';
+import 'package:flutter/animation.dart';
+
+import '../common.dart';
+
+const int _kNumIters = 10000;
+
+void _testCurve(Curve curve, {String name, String description, BenchmarkResultPrinter printer}) {
+  final Stopwatch watch = Stopwatch();
+  print('$description benchmark...');
+  watch.start();
+  for (int i = 0; i < _kNumIters; i += 1) {
+    final double t = i / _kNumIters.toDouble();
+    curve.transform(t);
+  }
+  watch.stop();
+
+  printer.addResult(
+    description: description,
+    value: watch.elapsedMicroseconds / _kNumIters,
+    unit: 'µs per iteration',
+    name: name,
+  );
+}
+
+void main() {
+  assert(false, "Don't run benchmarks in checked mode! Use 'flutter run --release'.");
+  final BenchmarkResultPrinter printer = BenchmarkResultPrinter();
+  _testCurve(
+    const Cubic(0.0, 0.25, 0.5, 1.0),
+    name: 'cubic_animation_transform_iteration',
+    description: 'Cubic animation transform',
+    printer: printer,
+  );
+
+  final CatmullRomCurve catmullRomCurve = CatmullRomCurve(const <Offset>[
+    Offset(0.09, 0.99),
+    Offset(0.21, 0.01),
+    Offset(0.28, 0.99),
+    Offset(0.38, -0.00),
+    Offset(0.43, 0.99),
+    Offset(0.54, -0.01),
+    Offset(0.59, 0.98),
+    Offset(0.70, 0.04),
+    Offset(0.78, 0.98),
+    Offset(0.88, -0.00),
+  ], tension: 0.00);
+  _testCurve(
+    catmullRomCurve,
+    name: 'catmullrom_transform_iteration',
+    description: 'CatmullRomCurve animation transform',
+    printer: printer,
+  );
+
+  printer.printToStdout();
+}

dev/benchmarks/microbenchmarks/lib/geometry/rrect_contains_bench.dart

@@ -14,8 +14,8 @@ void main() {
   print('RRect contains benchmark...');
   watch.start();
   for (int i = 0; i < _kNumIters; i += 1) {
-    final RRect outter = RRect.fromLTRBR(10, 10, 20, 20, const Radius.circular(2.0));
-    outter.contains(const Offset(15, 15));
+    final RRect outer = RRect.fromLTRBR(10, 10, 20, 20, const Radius.circular(2.0));
+    outer.contains(const Offset(15, 15));
   }
   watch.stop();