[libcxxabi] [llvm] [ItaniumDemangle] Add customizable printLeft/printRight APIs to OutputBuffer (PR #133249)

[Michael Buch via llvm-commits]

Michael137 wrote:

@zygoloid Added the suggested hooks in latest iteration. On the LLDB PR `insert` and `prepend` are pretty easy to handle (we just have to shift all the locations after the position that we've inserted into).

`setCurrentPosition` is trickier because we don't actually know what should happen to the tracked locations. I chose to just reset all the locations when that is called.

https://github.com/llvm/llvm-project/pull/133249