Don't use SubMonitor when saving project in SaveManager

The migration from the IProgressMonitor to the SubMonitor done as part
of 40114d2 also converts the progress
monitor used within the InternalMonitorWrapper.

If the parent monitor is a SubMonitor, this calls beginTask() both when
the InternalMonitorWrapper is created, as well as explicitly later on.
To avoid this, switch back to create a null-safe progress monitor via
Policy.monitorFor(...).

Closes #1758

Author: ptziegler

resources/bundles/org.eclipse.core.resources/src/org/eclipse/core/internal/resources/SaveManager.java

@@ -1,5 +1,5 @@
 /*******************************************************************************
- * Copyright (c) 2000, 2023 IBM Corporation and others.
+ * Copyright (c) 2000, 2025 IBM Corporation and others.
  *
  * This program and the accompanying materials
  * are made available under the terms of the Eclipse Public License 2.0
@@ -1188,7 +1188,7 @@ class InternalMonitorWrapper extends ProgressMonitorWrapper {
 		private boolean ignoreCancel;
 
 		public InternalMonitorWrapper(IProgressMonitor monitor) {
-			super(SubMonitor.convert(monitor));
+			super(Policy.monitorFor(monitor));
 		}
 
 		public void ignoreCancelState(boolean ignore) {