Draft LW2 spec

[Dan Smith]

Updated spec:

http://cr.openjdk.java.net/~dlsmith/lw2/lw2-20190628/specs/inline-classes-jvms.html

What's new?

- Specification for using "<init>" as a regular method name. Lots of choices to be made here, so I'm curious about how what I ended up with compares to what is currently implemented.

- Added some discussion blocks in various places, based on feedback.

- Changed required version numbers to 57.0.

- Static constraints on use of `ACC_INLINE`, declarations of instance initialization methods, and forms of CONSTANT_Class_infos appearing in various attributes and other places.

- Prohibited circularities in static field types.

- Added resolution checks on Q types in CONSTANT_Classes and CONSTANT_MethodTypes.

- Cleaned up the verification type diagram; fixed the verification type of 'this' in inline classes.

A few big things left to do, as described in the introduction.