Add generics to ast Annotation

[hduelme]

What it does

I added missing generics to Stack in the Annotation class

How to test

This doesn't change any behavior.

Author checklist

• [x] I have thoroughly tested my changes
• [x] The change is following the coding conventions
• [X] I have signed the Eclipse Contributor Agreement (ECA)

[stephan-herrmann]

At such narrow scope those changes are welcome indeed.

Out of curiosity, have you been investigating any bug in the code area?

[hduelme]

Not really a bug. I'm investigating a high CPU usage issue. This was just a discovery along the way.