Remove pointless parallel stream processing for classpath entries.

Since we already execute all calls to
NativeImageClassLoaderSupport.LoadClassHandler#handleClassFileName
via the ForkJoinPool.commonPool(), the use of parallelStream() here
does not further increase parallel execution and can be replaced
with a simple forEach without increasing class initialization time.

Additionally, avoiding parallelStream() fixes a deadlock that was
observable when only one CPU core is available (parallel streams
also use the commonPool() and this can lead to a deadlock with our
own use on single core systems).

Author: olpaw

substratevm/src/com.oracle.svm.hosted/src/com/oracle/svm/hosted/NativeImageClassLoaderSupport.java

@@ -817,7 +817,7 @@ private void run() {
                     initModule(moduleReference, true);
                 }
 
-                classpath().parallelStream().forEach(this::loadClassesFromPath);
+                classpath().forEach(this::loadClassesFromPath);
             } finally {
                 scheduledExecutor.shutdown();
             }