New lines are not stripped together with other whitespaces

[Reinmar]

On conversion from DOM -> view we don't strip new line characters.

TC: Create an editor on the following contents:

<div id="editor"><p>x</p></div>

<div id="editor"><p>x</p>
</div>

In the second case you'll have a <paragraph>\n</paragraph> in the model.

[Reinmar]

I guess it's something in DomConverter#_processDataFromDomText(). It'd be good to take a look on that because those new paragraphs are disturbing when using the editor in real cases.

[Reinmar]

OK... this is pretty bad. I wrote a couple of tests and most of them fail:

      ✖ new line at the end of content is ignored
      ✔ whitespaces at the end of content are ignored
      ✖ nbsp at the end of content is not ignored
      ✔ new line at the beginning of content is ignored
      ✔ whitespaces at the beginning of content are ignored
      ✖ nbsp at the beginning of content is not ignored
      ✖ new line between blocks is ignored
      ✔ whitespaces between blocks are ignored
      ✖ nbsp between blocks is not ignored
      ✖ new lines inside blocks are ignored
      ✔ whitespaces inside blocks are ignored
      ✔ nbsp inside blocks are not ignored
      ✖ all whitespaces together are ignored

[Reinmar]

This turned out to be really interesting.

Problems can be reproduced if there's just one whitespace between blocks or at the content boundary. But all works fine if there's more of them.

There's also a small problem that we don't support autoparagraphing  s. They are simply being ignored. I guess we can live with that so I won't work on fixing this bit (unless I'll find just the right place :D).

[Reinmar]

OK, there's one more important aspect, right now we turn all kind of spaces (\s) to normal spaces and later we normalise those. This is unsafe. I can see in CKE4 we use ltrim() and rtrim() which are limitted to [ \t\n\r].

I think that we should do the same in CKE5 because we may cause data loss in some languages or with special spaces being used intentionally.

[Reinmar]

Followup about nbsps: https://github.com/ckeditor/ckeditor5-engine/issues/987