Refactored common extension

[sean-gilliam]

All the DI assemblies had the same implementation of an extension.
Refactored the extension and moved it to Akka.DI.Core.

[sean-gilliam]

The build error looks to be TeamCity related and not PR related.

[21:08:37]Step 1/1: FAKE Build (Command Line) (49s)
[21:08:40][Step 1/1] Starting: D:\BuildAgent\temp\agentTmp\custom_script6376670813213844280.cmd
...
[21:08:54][Step 1/1] Unable to find version '3.4.1' of package 'FAKE'.
...
[21:09:27][Step 1/1] The system cannot find the path specified.
[21:09:27][Step 1/1] Process exited with code 3
[21:09:27][Step 1/1] Step FAKE Build (Command Line) failed

[Aaronontheweb]

@sean-gilliam I'll re-run the builds until I see a green check mark. Between racy unit tests (have an open issue for that - #853) and intermittent issues with NuGet sometimes (timeouts, yay!) it needs some human supervision sometimes.