abitidy: extract code to get a comment node into a separate function am: 9ee33c13f9

Original change: https://android-review.googlesource.com/c/platform/external/libabigail/+/2175523

Change-Id: Ib0faa5b0eb93c0841b31303afb3eab924a0591eb
Signed-off-by: Automerger Merge Worker <android-build-automerger-merge-worker@system.gserviceaccount.com>