Missing maven sources artifacts for internal classes

[dconnelly]

Describe the bug
Looks like source artifacts aren't attached for internal classes. This makes it more difficult for developers to help debug problems in the SDK, so would be a good idea to attach sources for all artifacts since we publish the source via GitHub anyway.

To Reproduce
Try and navigate to SDK internal class via IDE.

Expected behavior
Expect to see actual source file, vs IDE decompiled binary which is less informative.

Actual behavior
Only see decompiled binary in IDE if supported.

Environment summary
SDK Version: 2.6.5
Java JDK version: 11
OS Version (e.g. Windows, Linux, MacOSX) MacOSX