[llvm] [DebugInfo][RemoveDIs] Convert debug-info modes when loading bitcode (PR #78967)

[Jeremy Morse via llvm-commits]

jmorse wrote:

/me squints -- alright, this was because I was using `I.DbgMarker->getDbgValueRange()` rather than `I.getDbgValueRange()`, and I wasn't testing with a clean tree. I'd  reapply with the obvious fix, but I'm also out of the figurative office for the rest of the day, so can't revert if it kills all the buildbots again.

https://github.com/llvm/llvm-project/pull/78967