Delay delambdafication and put the lambda's body into the containing class

This is an experimental work in progress PR to bring us closer to using method handles. It will be entirely protected by a flag until it is as solid as the current mechanism.

With the flag enabled the compiler will defer final translation from lambda to class until very late in the pipeline, and it will put the body of the lambda in a method in the original class.

This PR leaves two key things undone

1) Specialization still needs to be handled.
2) Logic that partially prevents the use of 'this' in a super constructor call is bypassed. That logic needs to be redone in order to have fewer holes and be less brittle.

To enable on a one off basis use -Ydelambdafy:method. For extensive testing modify ScalaSettings to make "method" the default and recompile.

Resubmission of #2887