Take a strong widget to depend on, and use the question mark

`depend_on_size` took a bare `WidgetId`, which any id at all satisfies.
It takes a `&StrongWidget` now, so `DrawResult` carries the handle it
was drawn from rather than an id copied out of it and nothing can claim
a dependency on a widget it does not hold.

`UiSpan::outside` matched on a pair of `Option`s where `?` says it. It
was written that way while the method was still `const`, and it is not.

No call site changed. Checked: fmt, clippy and 35 tests; `tabs`, `view`,
`minimal` and `text` render unchanged, and the live sway resize round
trip still matches a cold start at each size.

core/src/orientation/pos.rs

@@ -279,10 +279,10 @@ impl UiSpan {
     }
 
     pub fn outside(&self, parent: &Self) -> Option<Self> {
-        match (self.start.outside(parent), self.end.outside(parent)) {
-            (Some(start), Some(end)) => Some(Self { start, end }),
-            _ => None,
-        }
+        Some(Self {
+            start: self.start.outside(parent)?,
+            end: self.end.outside(parent)?,
+        })
     }
 
     pub const fn len(&self) -> UiScalar {