Don't hard-code the line wrapping in backdrop_mail() and _backdrop_wrap_mail_line()

Description of the need

As reported on https://backdrop.zulipchat.com/#narrow/stream/218635-Backdrop/topic/How.... I tracked the lines are getting wrapped by backdrop_wrap_mail() following really outdated RFC standards and that breaks the format of messages read on modern mail clients.

Proposed solution

@albanycomputers (https://backdrop.zulipchat.com/#narrow/stream/218635-Backdrop/topic/How....):

The RFC Standard for emails are "old" to say the least and other techniques for manipulating emails have been developed, i.e. modern email clients and HTML encoding... etc..

So, I would agree, remove the hard coding and either leave it at that or add an option to wrap at line 80.

Hope this helps.

Alternatives that have been considered

I could not find any way of bypassing this wrapping at about 78 characters when I really need one of the projects to be sending continuous lines, letting the receiving client program do the correct wrapping.

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Useful resources

• https://stackoverflow.com/questions/2696433/is-it-necessary-to-wrap-long...
• backdrop_wrap_mail() is the function handling this (where the hard-coding happens)