Wrap long lines (follow up)

[lorenzwalthert]

Follow-up of #414.

[lorenzwalthert]

Status of this PR:

• worked at some point but not for all cases I experimented with.
• probably there are merge conflicts by now, has to be rebased on master. I think this PR is conceptually a good approach, but the implementation may need substantial rework.
• After the experience with caching and stylerignore feature in v1.3.0, I think we should make this an opt-in feature governed by an R option for a few releases. Also, styler will be slower when this is turned on.
• as this is considered to be invasive, it should only take effect for strict = TRUE.
• Not sure if we should takle the problem for different expression types individually instead of aiming for a general solution. Prime candidate: function calls. I think the overwhelming majority of long lines are function calls (potentially nested in assignment expressions). Related: Enforce line break after + in ggplot2 #544.

I am not going to contribute code to this feature soon though.