Reapply "[DebugInfo][RemoveDIs] Turn on non-instrinsic debug-info by default"

This reapplies commit bdde5f9.

The above commit previously failed due to buildbot errors:
  https://lab.llvm.org/buildbot/#/builders/205/builds/25126
  https://lab.llvm.org/buildbot/#/builders/184/builds/10242

These failures should have been respectively resolved by the commits:
  afa413a
  b5a273a

As noted in the original commit, this commit may break downstream tests.
If this commit is breaking your downstream tests, please see comment 12 in
[0], which documents the kind of variation in tests we'd expect to see from
this change and what to do about it.

[0] https://discourse.llvm.org/t/rfc-instruction-api-changes-needed-to-eliminate-debug-intrinsics-from-ir/68939

Author: SLTozer

llvm/lib/IR/BasicBlock.cpp

@@ -34,7 +34,7 @@ cl::opt<bool>
     UseNewDbgInfoFormat("experimental-debuginfo-iterators",
                         cl::desc("Enable communicating debuginfo positions "
                                  "through iterators, eliminating intrinsics"),
-                        cl::init(false));
+                        cl::init(true));
 
 DPMarker *BasicBlock::createMarker(Instruction *I) {
   assert(IsNewDbgInfoFormat &&