Extract tdef.is_related plus its overrides in tobjectdef, trecorddef and tstringdef into a new function def_is_related in unit defcmp.

defcmp.pas:
  + add new function "def_is_related" which combines the "is_related" overloads of "tobjectdef", "trecorddef" and "tstringdef" (it returns "false" for other def types which is what "tdef.is_related" did)
  * compare_defs_ext & compatible_childmethod_resultdef: change call from "x.is_related" to "def_is_related(x,...)"
symtype.pas, tdef:
  - remove "is_related" method
symdef.pas:
  - remove "is_related" in "tobjectdef", "trecorddef" and "tstringdef"
  * tobjectdef.needs_inittable: for checking whether a Corba interface somehow inherits from a IInterface don't use "is_related" anymore (we want to avoid the dependency after all), but mimic the necessary functionality of "def_is_related"
htypechk.pas, nadd.pas, ncal.pas, ncnv.pas, ngtcon.pas, nld.pas, optvirt.pas, pdecobj.pas, pdecvar.pas, pexpr.pas, pgenutil.pas:
  * change call from "x.is_related" to "def_is_related(x,...)"
symtable.pas
  + use unit defcmp
  * change call from "x.is_related" to "def_is_related(x,...)"
jvm/njvmcnv.pas, jvm/njvmflw.pas:
  * change call from "x.is_related" to "def_is_related(x,...)"



git-svn-id: http://svn.freepascal.org/svn/fpc/trunk@25847 3ad0048d-3df7-0310-abae-a5850022a9f2