[llvm-dwarfdump][locstats] Unify handling of inlined vars with no loc

The presence or absence of an inline variable (as well as formal
parameter) with only an abstract_origin ref (without DW_AT_location)
should not change the location coverage.

It means, for both:

DW_TAG_inlined_subroutine
  DW_AT_abstract_origin (0x0000004e "f")
  DW_AT_low_pc  (0x0000000000000010)
  DW_AT_high_pc (0x0000000000000013)
  DW_TAG_formal_parameter
    DW_AT_abstract_origin       (0x0000005a "b")

and,

DW_TAG_inlined_subroutine
   DW_AT_abstract_origin (0x0000004e "f")
   DW_AT_low_pc  (0x0000000000000010)
   DW_AT_high_pc (0x0000000000000013)

we should report 0% location coverage. If we add DW_AT_location,
for both cases the coverage should be improved.

Differential Revision: https://reviews.llvm.org/D96045