Use diamond, remove unnecessary public keyword on interfaces

[ggrossetie]

A little code cleanup in the extension package (to reduce the code changes in #715).

If you want to do a single commit to use diamond operator everywhere I can do it. I can also remove the unnecessary public keyword from interfaces at once ?

[robertpanzer]

Thanks!
We can also iterate and update the code in steps.
At the time I added the public modifier to the interface methods because there's also the private modifier now.