When attempting to use String Loading to download a file through Udon, if for whatever reason the download never completes, neither the success or error functions will be called without any indicator or way to know what's going on. This is different with Image Loading where there's a progress float that tells us the progress of the download.

This causes problems in practice because Udon will be waiting for a callback that will never be called, and we don't know if it's because of slow internet or a failure of the request that hasn't and will never thrown any error. Requesting parity for String Loading to be able to get the download progress, both so we can display the state to users as well as handle the scenario by providing fallback logic.