[Runtime] Don't fail conformances when the global actor hook is missing

When the concurrency library's "is current global actor" hook is not
available, assume that we are already executing on the right global
actor. This mimics the behavior of earlier standard libraries when
faced with an isolated conformance, as well as dealing with odd
configurations where the code might not load the concurrency library
yet

At the moment, WebAssembly ends up in this configuration because we
don't run the initialization for the concurrency library. That makes
this also a workaround for issue #82682 / rdar://154762027.

Author: DougGregor

stdlib/public/runtime/ProtocolConformance.cpp

@@ -1474,8 +1474,9 @@ static bool swift_isInConformanceExecutionContextImpl(
     return true;
 
   if (context->globalActorIsolationType) {
+    // If the hook is not installed, assume we're on the right actor.
     if (!_swift_task_isCurrentGlobalActorHook)
-      return false;
+      return true;
 
     // Check whether we are running on this global actor.
     if (!_swift_task_isCurrentGlobalActorHook(