Ensure VmService instance is disposed after failed direct connection attempt (#66123)

_attemptServiceConnection in FallbackDiscovery would fail if the root
library URI was not a package URI even if the VM service connection
attempt was successful. This resulted in a VM service connection being
left alive, causing DDS to fail its connection to the VM service.

Updated _attemptServiceConnection to ensure the VM service instance is
disposed after a non-connection related failure and to allow for root
library URIs with a file scheme.

packages/flutter_tools/lib/src/ios/fallback_discovery.dart

@@ -156,9 +156,10 @@ class FallbackDiscovery {
     // Attempt to connect to the VM service 5 times.
     int attempts = 0;
     Exception firstException;
+    VmService vmService;
     while (attempts < 5) {
       try {
-        final VmService vmService = await _vmServiceConnectUri(
+        vmService = await _vmServiceConnectUri(
           assumedWsUri.toString(),
         );
         final VM vm = await vmService.getVM();
@@ -167,15 +168,17 @@ class FallbackDiscovery {
             isolateRefs.id,
           );
           final LibraryRef library = isolateResponse.rootLib;
-          if (library != null && library.uri.startsWith('package:$packageName')) {
+          if (library != null &&
+             (library.uri.startsWith('package:$packageName') ||
+              library.uri.startsWith(RegExp(r'file:\/\/\/.*\/' + packageName)))) {
             UsageEvent(
               _kEventName,
               'success',
               flutterUsage: _flutterUsage,
             ).send();
 
-            // We absolutely must dispose this vmService instance, otherwise
-            // DDS will fail to start.
+            // This vmService instance must be disposed of, otherwise DDS will
+            // fail to start.
             vmService.dispose();
             return Uri.parse('http://localhost:$hostPort');
           }
@@ -184,6 +187,10 @@ class FallbackDiscovery {
         // No action, we might have failed to connect.
         firstException ??= err;
         _logger.printTrace(err.toString());
+      } finally {
+        // This vmService instance must be disposed of, otherwise DDS will
+        // fail to start.
+        vmService?.dispose();
       }
 
       // No exponential backoff is used here to keep the amount of time the