Support multiline Texts

[BafDyce]

See #182 . Since @karroffel assigned the Bug tag to it I tried to find the cause for it and develop a fix.

Some open questions:

• Do we also need to add scaled_font.line_gap() to the calculation?
• Are there other (unicode) symbols which are equivalent to \n (or have a similar function)?
• Are there any other control characters which we might need to support? (LTR, RTL, etc. ?)

[karroffel]

(I assigned the "bug" label because I would expect that to work 😄 )

There are more line separators, but with full unicode support and support for non-latin languages I think this might become super complex. Maybe there are layouting crates for displaying text that handle all this properly already?

Your patch seems good to me so far, I am just concerned that in order to deal with text properly a LOT of things need to be in place. I think supporting \n is definitely a good start but maybe we can be on the lookout for existing solutions.

[BafDyce]

Yeah, I totally agree. Text handling IS super complicated. Maybe we can just merge this one and open a new issue "Proper Text support" or something along the lines. Unfortunately, I'm not really experienced with string/text handling in rust and dont know which crates exist out there either.

[cart]

ab_glyph (the text library we use) has a simple paragraph layout example (which does use line_gap):
https://github.com/alexheretic/ab-glyph/blob/master/dev/src/layout.rs

We should probably also use that. This does seem like a good start and I'm fine making "full multiline support" an iterative process. I'll give this a full review soon.

[cart]

I'm going to merge this for now. Its a usability win and we can sort out line height later.

[DJMcNab]

@BafDyce We need you to respond in #2373 because of this PR.