lambda: Infrastructure to support capture/liberate-variable dex opcodes

* ArtLambdaMethod - wrap an ArtMethod with extra runtime lambda info
* Closure - data representation for a runtime lambda closure (read-only)
* ClosureBuilder - writer for creating a Closure at runtime
* ShortyFieldType - char/enum wrapper for shorty_field_type in dex

Tests:
* Closure, ClosureBuilder, ShortyFieldType have full unit test coverage.
* ArtLambdaMethod does not, but it is tested indirectly and is otherwise
  trivial getters.

Future CLs will include interpreter integration with minimal changes to
this Closure infrastructure.

Change-Id: I38a7aea8df1da7b154fd6623258c6c228c8e51df