Bug 1759163 - Add origin trial support for worklets. r=asuth

Move the trial getter to nsIGlobalObject, make every implementation
provide a reasonable value, and add a test.

Differential Revision: https://phabricator.services.mozilla.com/D140848

dom/base/nsGlobalWindowOuter.cpp

@@ -1698,6 +1698,11 @@ uint32_t nsGlobalWindowOuter::GetPrincipalHashValue() const {
   return 0;
 }
 
+OriginTrials nsGlobalWindowOuter::Trials() const {
+  return mInnerWindow ? nsGlobalWindowInner::Cast(mInnerWindow)->Trials()
+                      : OriginTrials();
+}
+
 nsresult nsGlobalWindowOuter::EnsureScriptEnvironment() {
   if (GetWrapperPreserveColor()) {
     return NS_OK;