[clang] [llvm] [reland][DebugInfo] Update DIBuilder insertion to take InsertPosition (PR #126967)

[Harald van Dijk via cfe-commits]

hvdijk wrote:

This is a reland of #126059 with `insertDeclare`'s overload taking `BasicBlock *` restored, and the changes to calls to that overload reverted. We previously had nothing that relied on its peculiar behavior, therefore the change in its behavior passed testing, but it crossed paths with #118314 which added a call that does rely in inserting not at the end of a block, but before the block's terminator.

https://github.com/llvm/llvm-project/pull/126967