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

This reapplies commit bdde5f9 by undoing the revert bc66e0c.

The previous reapplication 5c9f768 was reverted due to a crash
(reproducer in comments for 5c9f768) which was fixed in #81595.

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: OCHyams

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 &&