Refactor useful code from swank/abcl into ABCL-INTROSPECT

[easye]

In developing the introspection routines in SLIME swank/abcl, @alanruttenberg has added a fair amount of functionality in https://github.com/slime/slime/blob/master/swank/abcl.lisp that probably belongs in ABCL proper as it would benefit other such tools (SLY, et. al.)

The proper place to add this code is probably in the abcl-introspect contrib to avoid disturbing the low-level debugging facilities.

The scope of such a task is loosely defined but it could start with the eval-when constructs in swank/abcl which modify the behavior of functions in the sys package, moving them to be a consequence of loading abcl-introspect.

c.f. https://github.com/slime/slime/pull/563

[easye]

@alanruttenberg A general ticket for cleaning up the defadvice hooks in Swank by moving this into the load of abcl-introspect.