[google_maps_flutter_platform_interface] Pipe image size through mipmaps = false case

This is needed to support marker anchors since the Flutter API uses unit coordinates but the JS API uses pixels and the plugin doesn't otherwise need to decode the image so the size isn't otherwise available for the conversion.

Author: AsturaPhoenix

packages/google_maps_flutter/google_maps_flutter_platform_interface/lib/src/types/bitmap.dart

@@ -131,22 +131,26 @@ class BitmapDescriptor {
     bool mipmaps = true,
   }) async {
     final double? devicePixelRatio = configuration.devicePixelRatio;
+    final String asset;
+    final double scale;
+
     if (!mipmaps && devicePixelRatio != null) {
-      return BitmapDescriptor._(<Object>[
-        _fromAssetImage,
-        assetName,
-        devicePixelRatio,
-      ]);
+      asset = assetName;
+      scale = devicePixelRatio;
+    } else {
+      final AssetImage assetImage =
+          AssetImage(assetName, package: package, bundle: bundle);
+      final AssetBundleImageKey assetBundleImageKey =
+          await assetImage.obtainKey(configuration);
+      asset = assetBundleImageKey.name;
+      scale = assetBundleImageKey.scale;
     }
-    final AssetImage assetImage =
-        AssetImage(assetName, package: package, bundle: bundle);
-    final AssetBundleImageKey assetBundleImageKey =
-        await assetImage.obtainKey(configuration);
+
     final Size? size = configuration.size;
     return BitmapDescriptor._(<Object>[
       _fromAssetImage,
-      assetBundleImageKey.name,
-      assetBundleImageKey.scale,
+      asset,
+      scale,
       if (kIsWeb && size != null)
         <Object>[
           size.width,