[Debuginfo][NFC] Create common error handlers for DWARFContext.

Summary:
this review is extracted from D74308.

It creates two error handlers which allow to redefine error
reporting routine and should be used for all places
where errors are reported:

  std::function<void(Error)> RecoverableErrorHandler = defaultErrorHandler;
  std::function<void(Error)> WarningHandler = defaultWarningHandler;

It also creates accessors to above handlers which should be used to
report errors.

  function_ref<void(Error)> getRecoverableErrorHandler() {
    return RecoverableErrorHandler;
  }

  function_ref<void(Error)> getWarningHandler() { return WarningHandler; }

It patches all error reporting places inside DWARFContext and DWARLinker.

Reviewers: jhenderson, dblaikie, probinson, aprantl, JDevlieghere

Reviewed By: jhenderson, JDevlieghere

Subscribers: hiraditya, llvm-commits

Tags: #llvm, #debug-info

Differential Revision: https://reviews.llvm.org/D74481