Problem: too many STRLEN calls when getting a memline
Solution: Optimize calls to STRLEN(), add a few functions in memline.c
that return the byte length instead of relying on STRLEN()
(John Marriott)
closes: vim/vim#1405202d7a6c6cf
Cherry-pick line break changes from patch 8.1.0226.
Cherry-pick ml_line_len from patch 8.1.0579.
Cherry-pick test_comments.vim change from patch 9.1.0153.
Co-authored-by: John Marriott <basilisk@internode.on.net>