LibWeb: Add canvas context2d roundRect

Tests/LibWeb/Ref/canvas-path-rect.html

@@ -0,0 +1,40 @@
+<link rel="match" href="reference/canvas-path-rect-ref.html" />
+<style>
+  * {
+    margin: 0;
+  }
+  body {
+    background-color: white;
+  }
+</style>
+<canvas width=500 height=500></canvas>
+<script>
+    function drawRect() {
+        var canvas = document.querySelector("canvas");
+        var ctx = canvas.getContext("2d");
+        ctx.fillStyle = 'black';
+        ctx.fillRect(0, 0, 500, 500);
+
+        ctx.fillStyle = 'red';
+        ctx.beginPath();
+        ctx.rect(10, 20, 150, 100);
+        ctx.fill();
+
+        ctx.fillStyle = 'yellow';
+        ctx.beginPath();
+        ctx.roundRect(50, 310, 100, 100, 25);
+        ctx.fill('evenodd');
+
+        ctx.fillStyle = 'green';
+        ctx.beginPath();
+        ctx.rect(200, 210, 100, 100);
+        ctx.fill('evenodd');
+
+        ctx.rotate(0.2);
+        ctx.fillStyle = 'orange';
+        ctx.beginPath();
+        ctx.roundRect(325, 300, 100, 100, [ { x: 5, y: 20 }, 10, { x: 15, y: 30 }, 20 ]);
+        ctx.fill('evenodd');
+    }
+    drawRect();
+</script>

Tests/LibWeb/Ref/reference/canvas-path-rect-ref.html

@@ -0,0 +1,15 @@
+<style>
+    * {
+      margin: 0;
+    }
+    body {
+      background-color: white;
+    }
+  </style>
+  <!-- To rebase:
+    1. Open canvas-path-rect.html in Ladybird
+    2. Resize the window just above the width of the canvas
+    3. Right click > "Take Full Screenshot"
+    4. Update the image below:
+  -->
+  <img src="./images/canvas-path-rect-ref.png">