Improve sb2 unpackaging

Fixes:
- unpackaging raw sb2 (before we would return project.json but no assets and wrong type)
- unpackaging exe in https://gamejolt.com/games/Jazzcraft/474009

unpackager.js

@@ -245,27 +245,39 @@ var unpackage = (function() {
     const packagedZip = await unzipOrNull(blob);
 
     if (packagedZip) {
-      // Zip files generated by the TurboWarp Packager can have a project.json alongside the assets
+      // Raw sb2, raw sb3, and zip files generated by TurboWarp Packager have a project.json alongside the assets.
       const projectJSON = findFileInZip(packagedZip, 'project.json');
       if (projectJSON) {
-        // The project is an sb3 project.
         const innerFolderPath = getContainingFolder(projectJSON.name);
         const innerZip = packagedZip.folder(innerFolderPath);
 
+        let sb3Assets = 0;
+        let sb2Assets = 0;
+
         // Remove extra files that aren't part of the project but are in the same folder
-        // This matters for HTMLifier zips of Scratch 3 projects
+        // This removes extra files from HTMLifier zips of Scratch 3 projects
         for (const path of Object.keys(innerZip.files)) {
-          const isPartOfProject = (
-            path === 'project.json' ||
-            /^[a-f0-9]{32}\.[a-z0-9]{3}$/i.test(path)
-          );
-          if (!isPartOfProject) {
+          if (path === 'project.json') {
+            // keep
+          } else if (/^[a-f0-9]{32}\.[a-z0-9]{3}$/i.test(path)) {
+            // sb3 asset; keep
+            sb3Assets++;
+          } else if (/^[0-9]+\.[a-z0-9]{3}$/i.test(path)) {
+            // sb2 asset; keep
+            sb2Assets++;
+          } else {
             innerZip.remove(path);
           }
         }
 
+        // Guess project time based on assets because we can't reliably parse the JSON without
+        // importing @turbowarp/json. Only count as sb2 if we saw an sb2-style asset name and
+        // and nothing that looks like an sb3. sb3 is much more common so if we're unsure,
+        // we'll lean towards that if there's any ambiguity.
+        const type = sb2Assets > 0 && sb3Assets === 0 ? 'sb2' : 'sb3';
+
         return {
-          type: 'sb3',
+          type,
           data: await innerZip.generateAsync({
             type: 'arraybuffer',
             compression: 'DEFLATE'