[DebugInfo][SROA] Correct debug info for global variables in case of SROA

The existing handling produced crash for test case (attached with patch).
Now the function transferSRADebugInfo is modified to
  - Ignore the current variable if it starts after the current Fragment.
  - Ignore the current variable if it ends before the current Fragment.
  - Generate (!DIExpression()) if current variable completely fits the
    current Fragment.
  - Otherwise (as earlier), generate the DW_OP_LLVM_fragment in IR if current
    Fragment partially defines current variable.

Reviewed By: aprantl

Differential Revision: https://reviews.llvm.org/D121107