chore: use IsThreadingDisabled instead of browser only

Author: jeromelaban

src/OpenTelemetry/BatchExportProcessor.cs

@@ -167,7 +167,7 @@ private BatchExportWorker<T> CreateWorker()
     {
 #if NET
         // Use task-based worker for browser platform where threading may be limited
-        if (OperatingSystem.IsBrowser() || !this.useThreads)
+        if (ThreadingHelper.IsThreadingDisabled() || !this.useThreads)
         {
             return new BatchExportTaskWorker<T>(
                 this.circularBuffer,

src/OpenTelemetry/Internal/ThreadingHelper.cs

@@ -0,0 +1,15 @@
+// Copyright The OpenTelemetry Authors
+// SPDX-License-Identifier: Apache-2.0
+
+namespace OpenTelemetry.Internal;
+
+internal class ThreadingHelper
+{
+    internal static bool IsThreadingDisabled()
+    {
+        // if the threadpool isn't using threads assume they aren't enabled
+        ThreadPool.GetMaxThreads(out int workerThreads, out int completionPortThreads);
+
+        return workerThreads == 1 && completionPortThreads == 1;
+    }
+}

src/OpenTelemetry/Metrics/Reader/PeriodicExportingMetricReader.cs

@@ -113,7 +113,7 @@ private PeriodicExportingMetricReaderWorker CreateWorker()
     {
 #if NET
         // Use task-based worker for browser platform where threading may be limited
-        if (OperatingSystem.IsBrowser() || !this.useThreads)
+        if (ThreadingHelper.IsThreadingDisabled() || !this.useThreads)
         {
             return new PeriodicExportingMetricReaderTaskWorker(
                 this,