switch to a Document trait and introduce Script/Head/Style/Meta components (#2635)

* switch to a Document trait and introduce Script/Head/Style/Meta components

* Fix desktop title

* Insert special elements into the head during the inital SSR render

* Make all head component attributes optional

* hydrate head elements

* improve the server streaming head warning

* Document fullstack head hydration approach

* deduplicate head elements by href

* move Link into head::Link

* document head components

* add meta and title examples

* Fix a few doc examples

* fix formatting

* Add title to playwright tests

* serde is optional on web, but it is enabled by hydrate

* remove leftover console log

packages/html/src/ts/head.ts

@@ -0,0 +1,19 @@
+// Helper functions for working with the document head
+
+function createElementInHead(
+  tag: string,
+  attributes: [string, string][],
+  children: string | null
+): void {
+  const element = document.createElement(tag);
+  for (const [key, value] of attributes) {
+    element.setAttribute(key, value);
+  }
+  if (children) {
+    element.appendChild(document.createTextNode(children));
+  }
+  document.head.appendChild(element);
+}
+
+// @ts-ignore
+window.createElementInHead = createElementInHead;