Draw a texture handle as the primitive it is

`Painter::primitive` takes `impl PrimitiveLike`: a primitive, or something
that yields one and does whatever else drawing it needs. A `&TextureHandle`
yields a `TexturePrimitive` and retains its share on the way through, so
`texture`, `texture_within` and `texture_at` are gone and an image is drawn
like anything else.

I said last round that the blanket impl would collide with the one for
`&TextureHandle` under coherence. It does not: `Primitive` is ours, so no
crate can add the impl that would overlap, and rustc accepts both.

Co-Authored-By: Claude Opus 5 <noreply@anthropic.com>

src/widget/image.rs

@@ -7,7 +7,7 @@ pub struct Image {
 
 impl Widget for Image {
     fn draw(&mut self, painter: &mut Painter) {
-        painter.texture(&self.handle);
+        painter.primitive(&self.handle);
     }
 
     fn desired_width(&mut self, _: &mut SizeCtx) -> Len {