Migrate item_foreign_type to Askama

[sladyn98]

This PR migrates item_foreign_type to Askama
Refers : #108868

[rustbot]

r? @GuillaumeGomez

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[GuillaumeGomez]

Let's wait for #112030 (comment) to be solved first.

[sladyn98]

Here render attributes expects a buffer so we might have to create one here or change the implementation of render_attributes in code to take both a buffer and an impl write

render_attributes_in_code(w, it, cx.tcx());
     |         ------------------------- ^ expected `&mut Buffer`, found `&mut impl fmt::Write`
     |         |
     |         arguments to this function are incorrect
     |

How we could modify render_attributess_in_code

enum WriteWrapper<'a> {
    Buffer(&'a mut html::format::Buffer),
    Writer(&'a mut dyn fmt::Write),
}

impl fmt::Write for WriteWrapper<'_> {
    fn write_str(&mut self, s: &str) -> fmt::Result {
        match self {
            WriteWrapper::Buffer(buffer) => buffer.write_str(s),
            WriteWrapper::Writer(writer) => writer.write_str(s),
        }
    }
}

fn render_attributes_in_code(w: &mut WriteWrapper<'_>, it: &clean::Item, tcx: TyCtxt<'_>) {
    for a in it.attributes(tcx, false) {
        write!(w, "<div class=\"code-attribute\">{}</div>", a);
    }
}

[GuillaumeGomez]

Or you can update render_attributes_in_code to make it take a impl Write instead of Buffer. ;)

fn render_attributes_in_code(w: &mut Buffer, it: &clean::Item, tcx: TyCtxt<'_>) {
    for a in it.attributes(tcx, false) {
        write!(w, "<div class=\"code-attribute\">{}</div>", a);
    }
}

[GuillaumeGomez]

(Unless I missed something obvious, Buffer implements Write so it should be the only change required?)

[nicklimmm]

We can actually remove the use of Buffer here and only rely on write!().

Recently, I made a change (to be merged soon) on render_attributes_in_code() that doesn't have Buffer nor impl Write in its input. Instead, it returns impl Display, which then can be used for write!().

See the change here

[GuillaumeGomez]

Please fix merge conflicts.

[sladyn98]

I will reopen this PR in a different commit, currently was just experimenting with my config.toml, which cause codgen to break.