LibWeb: Implement grid-template function fit-content()

Author: https://github.com/EdwinHoksberg
Commit: e5deaa1c07
Pull-request: https://github.com/LadybirdBrowser/ladybird/pull/815
Reviewed-by: https://github.com/kalenikaliaksandr ✅

Tests/LibWeb/Layout/input/grid/fit-content-1.html

@@ -0,0 +1,15 @@
+<style>
+.container {
+    display: grid;
+    background-color: lightsalmon;
+    grid-template-columns: fit-content(150px) fit-content(150px);
+}
+
+.one {
+    background-color: lightblue;
+}
+
+.two {
+    background-color: yellowgreen;
+}
+</style><div class="container"><div class="one">1</div><div class="two">2</div></div>

Tests/LibWeb/Layout/input/grid/fit-content-2.html

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+<style>
+#container {
+  display: grid;
+  grid-template-columns: fit-content(300px) fit-content(300px) 1fr;
+  grid-gap: 5px;
+  box-sizing: border-box;
+  height: 200px;
+  width: 100%;
+  background-color: #8cffa0;
+  padding: 10px;
+}
+
+#container > div {
+  background-color: #8ca0ff;
+  padding: 5px;
+}
+</style><div id="container">
+<div>Item as wide as the content.</div>
+<div>
+Item with more text in it. Because the contents of it are wider than the
+maximum width, it is clamped at 300 pixels.
+</div>
+<div>Flexible item</div>
+</div>
+