Add DrawTarget::{measure_text/measure_glyphs}

[l4l]

I'm not sure about API though, it looks quite clumsy now. Besides, do you mind if I run rustfmt at separate PR and add it to CI? It's quite clumsy to turn it off only for that project :\

Besides, I may extend examples/capabilities.rs with this:

let offset = dt.measure_text(
    &font,
    24.,
    "Hello",
    AntialiasMode::Gray,
).expect("measure_text failed");

dt.draw_text(
    &font,
    24.,
    "World",
    Point::new(offset.size.width as f32, 124.),
    &Source::Solid(SolidSource {
        r: 0,
        g: 0,
        b: 0xff,
        a: 0xff,
    }),
    &DrawOptions::new(),
);

(and with removing "photo.png" reading) the result image will be the following:

Details

Closes #169

[l4l]

Any comment on this, @jrmuizel? Would really like to merge this, so I can switch out to upstream from my fork.

[jrmuizel]

I'm not in a rush to expand the text handling stuff much. Is it possible for you to measure/layout your text using a proper shaping library? Like skribo, rustybuzz, or allsorts?

[l4l]

Sure, that make sense, thanks for a handy create list, I'll try them out.

Do you generally opposed to any new text rendering features in raqote? Imo current text feature looks really limited, shouldn't it be removed in favor of generic and backend-agnostic (e.g. with consideration of #174) way of font render (like getting a canvas for a given width)?

And also, what's the status of #169 then? Should it be closed with "wont fix" status?