Render a context menu when right-clicking in project panel

It doesn't currently do anything, but I managed to get it rendering in an absolutely positioned way.

crates/gpui/src/elements/overlay.rs

@@ -1,16 +1,28 @@
+use serde_json::json;
+
 use crate::{
     geometry::{rect::RectF, vector::Vector2F},
+    json::ToJson,
     DebugContext, Element, ElementBox, Event, EventContext, LayoutContext, PaintContext,
     SizeConstraint,
 };
 
 pub struct Overlay {
     child: ElementBox,
+    abs_position: Option<Vector2F>,
 }
 
 impl Overlay {
     pub fn new(child: ElementBox) -> Self {
-        Self { child }
+        Self {
+            child,
+            abs_position: None,
+        }
+    }
+
+    pub fn with_abs_position(mut self, position: Vector2F) -> Self {
+        self.abs_position = Some(position);
+        self
     }
 }
 
@@ -23,6 +35,11 @@ impl Element for Overlay {
         constraint: SizeConstraint,
         cx: &mut LayoutContext,
     ) -> (Vector2F, Self::LayoutState) {
+        let constraint = if self.abs_position.is_some() {
+            SizeConstraint::new(Vector2F::zero(), cx.window_size)
+        } else {
+            constraint
+        };
         let size = self.child.layout(constraint, cx);
         (Vector2F::zero(), size)
     }
@@ -34,9 +51,10 @@ impl Element for Overlay {
         size: &mut Self::LayoutState,
         cx: &mut PaintContext,
     ) {
-        let bounds = RectF::new(bounds.origin(), *size);
+        let origin = self.abs_position.unwrap_or(bounds.origin());
+        let visible_bounds = RectF::new(origin, *size);
         cx.scene.push_stacking_context(None);
-        self.child.paint(bounds.origin(), bounds, cx);
+        self.child.paint(origin, visible_bounds, cx);
         cx.scene.pop_stacking_context();
     }
 
@@ -59,6 +77,10 @@ impl Element for Overlay {
         _: &Self::PaintState,
         cx: &DebugContext,
     ) -> serde_json::Value {
-        self.child.debug(cx)
+        json!({
+            "type": "Overlay",
+            "abs_position": self.abs_position.to_json(),
+            "child": self.child.debug(cx),
+        })
     }
 }