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

[Richard Smith via llvm-commits]

================
@@ -121,6 +137,8 @@ class OutputBuffer {
   OutputBuffer &prepend(std::string_view R) {
     size_t Size = R.size();
 
+    notifyInsertion(/*Position=*/0, /*Count=*/Size);
----------------
zygoloid wrote:

I think this should be called after we perform the insert, so that the callback can inspect the added bytes.

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