filesystem permissions: limit number of startup permissions checks

This is way too slow with a large number of files. The majority of the
files on my system are screenshots, which are not important since we do
not read or write from them.

Most of the time seems to be in isWritable() which is doing GetFileSecurity(),
OpenThreadToken(), and AccessCheck().

Limit the checks to the main top level directories and then also limit
the number of files checked in each directory.

src/main/java/net/runelite/launcher/FilesystemPermissions.java

@@ -24,6 +24,7 @@
  */
 package net.runelite.launcher;
 
+import com.google.common.base.Stopwatch;
 import java.io.File;
 import java.io.IOException;
 import java.nio.file.Files;
@@ -43,6 +44,7 @@ class FilesystemPermissions
 	// https://learn.microsoft.com/en-us/windows/win32/secauthz/well-known-sids
 	private static final String SID_SYSTEM = "S-1-5-18";
 	private static final String SID_ADMINISTRATORS = "S-1-5-32-544";
+	private static final int MAX_FILES_PER_DIRECTORY = 64;
 
 	static boolean check()
 	{
@@ -70,7 +72,10 @@ static boolean check()
 
 				// Files.walk is depth-first, which doesn't work if the permissions on the root don't allow traversal.
 				// So we do our own walk.
+				Stopwatch sw = Stopwatch.createStarted();
 				setTreeACL(RUNELITE_DIR, sid);
+				sw.stop();
+				log.debug("setTreeACL time: {}", sw);
 			}
 			catch (Exception ex)
 			{
@@ -122,7 +127,12 @@ static boolean check()
 			}
 		}
 
-		if (!checkPermissions(RUNELITE_DIR))
+		Stopwatch sw = Stopwatch.createStarted();
+		boolean permissionsOk = checkPermissions(RUNELITE_DIR, true);
+		sw.stop();
+		log.debug("checkPermissions time: {}", sw);
+
+		if (!permissionsOk)
 		{
 			String message;
 			if (elevated)
@@ -150,21 +160,30 @@ static boolean check()
 		return false;
 	}
 
-	private static boolean checkPermissions(File tree)
+	private static boolean checkPermissions(File tree, boolean root)
 	{
+		// Directory traversal and isWritable() is very slow. On my system checking 16k files
+		// takes ~13 seconds with traversal. The majority of these files tend to be screenshots
+		// which are less interesting.
+		//
+		// Traverse only the top level directories, and limit the number of files checked,
+		// to keep it speedy. The primary files which prevent the launcher and client from
+		// working are all here (repository2, cache, logs, profiles2).
 		boolean ok = true;
+		int numFiles = 0;
 		for (File file : tree.listFiles())
 		{
 			if (file.isDirectory())
 			{
-				if (!checkPermissions(file))
+				if (root && !checkPermissions(file, false))
 				{
 					ok = false;
 				}
 			}
-			else
+			else if (numFiles++ < MAX_FILES_PER_DIRECTORY)
 			{
 				Path path = file.toPath();
+				log.debug("Checking permissions of {}", path);
 				if (!Files.isReadable(path) || !Files.isWritable(path))
 				{
 					log.error("Permissions for {} are incorrect. Readable: {} writable: {}",