Fix the format=flowed; delsp=yes encoding of email messages

Can we provide examples in the summary for how this is better?

Thanks

@smustgrave I fleshed out part of the steps to reproduce a bit. If we need more, maybe you can clarify what you would like an example of.

Vastly improved display of email messages in email clients

can we get screenshots of the improvements

Ok I added some screenshots for the default out-of-the-box mailer, with and without the patch applied. (The other bug fixed by this patch is that the body is soft-wrapped but words are stuck together due to missing space; I didn't yet dig into how to reproduce it, but I suspect it could happen with a non-default mailer setup.)

Thanks, examples seem good improvements.

I read the issue summary, comments and the MR. Just about everything here is in order. It would be better if the screenshots were available from the issue summary but there are only 8 comments so far, so they are not hard to find. There are no unanswered questions. The comments in the MR are clear and easy to understand.

Leaving at RTBC

Embedding the screenshots.

Made a change to the issue summary... originally it sounded like this needed to be postponed on reverting another issue, but the issue was committed in 2013, so what is actually proposed here is to undo the change from that issue and implement a different fix instead. The situation was further confused by the fact that a better fix was proposed for Drupal 7 but not for Drupal 8, violating the backport policy. :)

An important thing to understand for this issue (which I had to re-read the summary to get) is that MailFormatHelper::htmlToText() already calls MailFormatHelper::wrapMail(), so the second call in the PHP mailer was redundant.

NW for the above comments/suggestions I posted on the MR, which should get reviewed by @mfb or another previous issue contributor (i.e., credit will not be granted to someone doing a drive-by application of my suggestions). Thanks!

Thanks @xjm, I further clarified the comments.

Feedback appears to be reviewed by @mfb mvoing back to RTBC.