[Android] Refine reflection generator to support generic types

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.
[Android] Fix that static method doesn't have comments

Those comments are for javadoc to generate documentation.
Merge pull request #2454 from wang16/reflection_generic_types

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