Handle cloud storage file extensions with versioning.

If a user uses its own IOSystem/IOStream for handling google cloud
storage or aws s3 uris, with this PR the extension will still be correct.

code/Common/BaseImporter.cpp

@@ -267,6 +267,12 @@ std::string BaseImporter::GetExtension(const std::string &file) {
     std::string ret = file.substr(pos + 1);
     ret = ai_tolower(ret);
 
+    // gcs uris (e.g. `gs://bucket/obj.glb#1234`) or aws s3 uris (e.g. `s3://bucket/obj.glb#NULL`)
+    // can have a version string at the end, remove it as well,
+    // so an underlying IOSystem/IOStream supporting gcs or aws s3 can handle it
+    // (see https://github.com/GoogleCloudPlatform/gsutil/blob/c80f329bc3c4011236c78ce8910988773b2606cb/gslib/storage_url.py#L39-L42)
+    ret = ret.substr(0, ret.find_last_of('#'));
+
     return ret;
 }