Bundle geckodriver for Linux in Tor Browser output

I was looking at tor-browser-selenium for a non-performance-measurement related task and got told to "Install geckodriver from the geckodriver releases page". I could not find any GPG signature or some other way to authenticate the binary (apart from having it fetched over TLS) which makes me feel a bit uneasy.

So, how about building geckodriver during our build and bundle it in our release directory as we do for other auxiliary tools as well? Another benefit of doing so is having always the proper geckodriver available for running a respective Tor Browser. No need anymore to figure out which of the download options from the website to choose from with the risk of running into weird errors. The costs are additional size for the whole browser directory (although only 2MB per arch) and slightly higher code complexity.

I can work on that ticket of a patch would be accepted.