wgsl: add refract as a built-in function (#1901)

SHA: 73c5ac1
Reason: push, by @Kangz

Co-authored-by: github-actions[bot] <41898282+github-actions[bot]@users.noreply.github.com>

index.html

@@ -1489,7 +1489,7 @@
 </style>
   <meta content="Bikeshed version 3d6a6fcbb, updated Wed Jun 16 16:19:39 2021 -0700" name="generator">
   <link href="https://www.w3.org/TR/webgpu/" rel="canonical">
-  <meta content="35167939981fc6b6c925e21d69bb94a5e23b12c0" name="document-revision">
+  <meta content="73c5ac1a3818f8dce9f450c372e556087552af67" name="document-revision">
 <style>
 /* Make <dl> blocks more distinct from their surroundings. */
 main dl:not(.switch) {
@@ -2230,7 +2230,7 @@
   <div class="head">
    <p data-fill-with="logo"><a class="logo" href="https://www.w3.org/"> <img alt="W3C" height="48" src="https://www.w3.org/StyleSheets/TR/2016/logos/W3C" width="72"> </a> </p>
    <h1 class="p-name no-ref" id="title">WebGPU</h1>
-   <h2 class="no-num no-toc no-ref heading settled" id="profile-and-date"><span class="content">Editor’s Draft, <time class="dt-updated" datetime="2021-07-06">6 July 2021</time></span></h2>
+   <h2 class="no-num no-toc no-ref heading settled" id="profile-and-date"><span class="content">Editor’s Draft, <time class="dt-updated" datetime="2021-07-07">7 July 2021</time></span></h2>
    <div data-fill-with="spec-metadata">
     <dl>
      <dt>This version: