fix(chrome): emit every markup attribute and read checked and selected off the property

the dump emitted a fixed standard attribute set, so a spec reading data-cents or data-account-id saw undefined on the goja host and nothing at all in the trace. it now keys every attribute by the name the markup writes, derived keys overwriting. checked and selected come from the dom property rather than whatever a component left on the object, which is also what the page-side element handle now reports, so a ticked box reads as ticked instead of reporting its starting state forever.

internal/driver/chrome/testdata/custom-element-flags.html

@@ -0,0 +1,22 @@
+<!doctype html>
+<html id="page">
+  <head id="page-head">
+    <meta id="page-charset" charset="utf-8" />
+    <title id="page-title">custom element flags</title>
+  </head>
+  <body id="page-body">
+    <div id="tabs">
+      <a id="tab-all" href="#/">All</a>
+      <a id="tab-active" href="#/active">Active</a>
+    </div>
+    <div id="picker"></div>
+    <input id="toggle" type="checkbox" checked />
+    <script id="page-script">
+      // What a component keeps in these properties is whatever the component
+      // means by them: a selector element names the selected item here rather
+      // than saying whether it is itself selected.
+      document.getElementById('tabs').selected = 'active';
+      document.getElementById('picker').checked = 'partial';
+    </script>
+  </body>
+</html>