Rename Java files to match public class names

[charlesrchance]

Fixes maven compilation

[pat-clark-avalara]

@charlesrchance - thanks for opening this MR. We're in the process of updating these SDKs. On the backend, we do some post-processing before the code makes it to this repository, so we don't usually make changes directly to this repo. I've noted your changes in your commit and I'll pull them into the next java SDK update. Thank you again!