Reign in XS portions needed for certain perls under debugging, several things:

Reign in XS portions needed for certain perls under debugging, several things:

- Do not rely on Sub::Identify at all (it is too finicky) - either use
  Sub::Util::subname if already loaded, or just use B (RT#96945)

- Allow either Sub::Name or Sub::Util to be used for namings

- Only add Sub::Name to the install list if neither Sub::* is available

- Clarify constant names, move them to _Util, make sure we use them everywhere

- Make sure that t/07-debugger.t runs on all perls, including the ones not
  needing the XS dance