Always send Origin header for non-HEAD/GET CORS fetches

In particular when they are same-origin.

Tests: web-platform-tests/wpt#36332.

Fixes #1022.

Author: evilpie

fetch.bs

@@ -3016,7 +3016,8 @@ given a <a for=/>request</a> <var>request</var>, run these steps:
 
   <ol>
    <li>
-    <p>Switch on <var>request</var>'s <a for=request>referrer policy</a>:
+    <p>If <var>request</var>'s <a for=request>mode</a> is not "<code>cors</code>",
+    then switch on <var>request</var>'s <a for=request>referrer policy</a>:
 
     <dl class=switch>
      <dt>"<code>no-referrer</code>"