[Android] Refine reflection generator to support generic types and comments for static methods

For latest Embedding API: onCreateWindowRequest,
ValueCallback<XWalkView> is introduced as its parameter, it
requires the reflection generator to support generic type.

Previous together with the implementation of this API, there
is a hard code solution for ValueCallback.
This is a more general handling for generic types.

The second commit is to fix that static method doesn't have comments for javadoc.