Merge branch 'jc/log-graph-simplify'

The implementation of "git log --graph" got refactored and then its output got simplified. * jc/log-graph-simplify: t4215: use helper function to check output graph: fix coloring of octopus dashes graph: flatten edges that fuse with their right neighbor graph: smooth appearance of collapsing edges on commit lines graph: rename `new_mapping` to `old_mapping` graph: commit and post-merge lines for left-skewed merges graph: tidy up display of left-skewed merges graph: example of graph output that can be simplified graph: extract logic for moving to GRAPH_PRE_COMMIT state graph: remove `mapping_idx` and `graph_update_width()` graph: reduce duplication in `graph_insert_into_new_columns()` graph: reuse `find_new_column_by_commit()` graph: handle line padding in `graph_next_line()` graph: automatically track display width of graph lines