[DebugInfo] Support for DW_AT_associated and DW_AT_allocated.

Summary:
This support is needed for the Fortran array variables with pointer/allocatable
attribute. This support enables debugger to identify the status of variable
whether that is currently allocated/associated.

  for pointer array (before allocation/association)
  without DW_AT_associated

(gdb) pt ptr
type = integer (140737345375288:140737354129776)
(gdb) p ptr
value requires 35017956 bytes, which is more than max-value-size

  with DW_AT_associated

(gdb) pt ptr
type = integer (:)
(gdb) p ptr
$1 = <not associated>

  for allocatable array (before allocation)

  without DW_AT_allocated

(gdb) pt arr
type = integer (140737345375288:140737354129776)
(gdb) p arr
value requires 35017956 bytes, which is more than max-value-size

  with DW_AT_allocated

(gdb) pt arr
type = integer, allocatable (:)
(gdb) p arr
$1 = <not allocated>

    Testing
- unit test cases added
- check-llvm
- check-debuginfo

Reviewed By: aprantl

Differential Revision: https://reviews.llvm.org/D83544