Revert "[BasicBlockUtils] Remove redundant llvm.dbg instructions after blocks...

Revert "[BasicBlockUtils] Remove redundant llvm.dbg instructions after blocks to reduce compile time (#89069)"

This reverts commit 2e3e0868. It caused
quadratic slowdown at compilation time in some cases. See the comments
in the original PR: https://github.com/llvm/llvm-project/pull/89069