BUG Fix utf8 non-latin characters generating invalid encoding

[tractorcow]

Related to silverstripe/silverstripe-graphql#318

I have tracked a text encoding issue where DBHTMLText::Plain() was mangling encoding of utf-8 non-latin text.

I have added a unit test, but I couldn't quite replicate the bug in the test without dumping the entire content area of my client's website (which, for confidentiality cases, obviously I can't push to github).

This fix replicates the same UTF-8 treatment in Convert::nl2os, which also adds this flag.

Without this fix, elemental module crashes the CMS when dealing with asian characters. I would put this at a high severity. :)

[GuySartorelli]

Without this fix, elemental module crashes the CMS when dealing with asian characters. I would put this at a high severity. :)

I can't reproduce that with silverstripe/framework 5.2 and dnadesign/silverstripe-elemental 5.2

I know this is quite old, but if it's a genuine problem and affects Silverstripe CMS 5 I'd like to see it resolved - can you please check if this is still a problem, and if so, provide clear reproduction steps?

If you need to provide some content confidentially I'm happy to receive it by email or slack, if that's suitable.

[GuySartorelli]

Closing as I can't reproduce and no more information has been provided after several months.