Show orphan definitions in stats

[st0012]

In the DSL processing PR, I noticed that many definitions are orphaned. Having stats like this will help us identify and fix the issue faster in the future.

Example output:

Definition breakdown:
  Type                    Total   Linked   Orphan
  ----                    -----   ------   ------
  Method                 360084   360083        1
  InstanceVariable       215153   215139       14
  Module                 197218   197217        1
  Class                  112067   112063        4
  Constant                65490    65478       12
  AttrReader              36903    36902        1
  SingletonClass          15999    15994        5
  AliasMethod              7166     7166        0
  AttrAccessor             6425     6425        0
  ConstantAlias            3745     3744        1
  ClassVariable             856      856        0
  AttrWriter                419      419        0
  GlobalVariable             36       36        0
  ----                    -----   ------   ------
  TOTAL                 1021561  1021522       39
  Orphan rate: 0.0%

[vinistock]

I'm not opposed to these stats, but it would be nice if we knew the names or location of definitions that ended up orphaned, so that we can more easily investigate

[st0012]

I've opened #563 for adding such feature