add code lens to explain expressions using Copilot to AOP related annotations

[martinlippert]

We can broaden the scope of the "explain with Copilot" feature to AOP related annotations.

The details:

• @Pointcut("..") -> explain the AspectJ pointcut expression ".."
• @Before(".."), @Around(".."), @After("..") -> explain the AspectJ before/around/after annotation expression ".."

[martinlippert]

Completed via #1338