annotate: add a new experimental --skip option to skip revs This option is most useful for mechanical code modifications, especially ones that retain the same number of lines.

annotate: add core algorithm to skip a rev The core algorithm is inspired by git hyper-blame, implemented at https://chromium.googlesource.com/chromium/tools/depot_tools.git/+/master/git_hyper_blame.py. The heuristic is as documented in the comments.