Lines in API reference XML files are too long

The lines in XML files in API reference are way too long. This causes several fairly minor, but noticeable annoyances to contributors like me:

* When viewing the source or editing it on GitHub, I have to keep scrolling horizontally.
* When viewing PRs or diffs, I have to switch to Split mode to see the differences without horizontal scrolling.
* I *think* that long lines mean that GitHub does not highlight which words changed (see e.g. the diff for https://github.com/dotnet/docs/pull/1930 and try to figure out what changed in remarks; compare it with https://github.com/svick/core-docs/commit/24815ef579a171f8a9913625148ee7ef0743afbb).

My questions (similar to those in https://github.com/dotnet/docs/issues/1951):

* Is this something that's worth fixing (considering it would change many files)?
* Would a PR by me be welcome, or do you have a better way to deal with this?
* Should it be fixed all at the same time, or would some kind of gradual process make more sense?
* Would it help to fix this in the same PR as https://github.com/dotnet/docs/issues/1951?

I have a work-in-progress code that would fix this [here](https://github.com/svick/ApiReferenceCleanup/blob/master/Program.cs). In case this is deemed worth doing, I would finish it and submit a PR.