We should have an option to ignore nonconflicting redundant lines

[eggrobin]

Our strategy for handling merge conflicts (previously: #444, #568, #583) is to ignore the conflict markers and interpret both branches. This is fine unless there is overlap between modified ranges, as happened to me recently while synchronizing #578; in that case, even if the overlap agrees, we need to manually merge ranges, which is error-prone (recall that we expect to have to juggle upwards of 50 of those PRs for a long time).

There are Merge objects passed around in PropertyParsingInfo, null in many places; we could replace those nulls with something that accepts consistent values, maybe behind a flag so we do that only when handling merge conflicts.

[macchiati]

Good idea. Could even do it for all dev versions that are regenerated, automatically.