[codegen] shallow/deep copy support for Java

[izgzhen]

TODO: state when & where it is needed and its importance

[Calvin-L]

Could you clarify what the scope of this issue is?

Some things you might mean, but I am not sure:

• Cozy-synthesized classes should be copy-able
• The inner classes that Cozy defines should be copy-able
• There should be facilities inside Cozy's own codegen infrastructure for making deep or shallow copies

[izgzhen]

I think I mean "There should be facilities inside Cozy's own codegen infrastructure for making deep or shallow copies".

[izgzhen]

needs more motivation. WONTFIX.