remove context from ui (again) and create weird trait for it

src/core/text.rs

@@ -116,10 +116,10 @@ impl TextBuilder {
     }
 }
 
-impl<Ctx> FnOnce<(&mut Ui<Ctx>,)> for TextBuilder {
+impl FnOnce<(&mut Ui,)> for TextBuilder {
     type Output = Text;
 
-    extern "rust-call" fn call_once(self, args: (&mut Ui<Ctx>,)) -> Self::Output {
+    extern "rust-call" fn call_once(self, args: (&mut Ui,)) -> Self::Output {
         let mut buf =
             TextBuffer::new_empty(Metrics::new(self.attrs.font_size, self.attrs.line_height));
         buf.set_text(