Replace StringBuffer with StringBuilder in ClasspathComputer3_0

The local variable `buffer` is not shared across threads, so
StringBuilder is the appropriate choice and avoids unnecessary
synchronization overhead.

Co-authored-by: Copilot <223556219+Copilot@users.noreply.github.com>

Author: laeubi

build/org.eclipse.pde.build/src/org/eclipse/pde/internal/build/builder/ClasspathComputer3_0.java

@@ -202,7 +202,7 @@ private void recordRequiredIds(BundleDescription model) {
 			bundleProperties = new Properties();
 			model.setUserObject(bundleProperties);
 		}
-		StringBuffer buffer = new StringBuffer();
+		StringBuilder buffer = new StringBuilder();
 		for (Long requiredId : requiredIds) {
 			buffer.append(requiredId.toString());
 			buffer.append(':');