Add initial element inspector for Zed development (#31315)

Open inspector with `dev: toggle inspector` from command palette or
`cmd-alt-i` on mac or `ctrl-alt-i` on linux.

https://github.com/user-attachments/assets/54c43034-d40b-414e-ba9b-190bed2e6d2f

* Picking of elements via the mouse, with scroll wheel to inspect
occluded elements.

* Temporary manipulation of the selected element.

* Layout info and JSON-based style manipulation for `Div`.

* Navigation to code that constructed the element.

Big thanks to @as-cii and @maxdeviant for sorting out how to implement
the core of an inspector.

Release Notes:

- N/A

---------

Co-authored-by: Antonio Scandurra <me@as-cii.com>
Co-authored-by: Marshall Bowers <git@maxdeviant.com>
Co-authored-by: Federico Dionisi <code@fdionisi.me>

crates/gpui/src/scene.rs

@@ -1,6 +1,9 @@
 // todo("windows"): remove
 #![cfg_attr(windows, allow(dead_code))]
 
+use schemars::JsonSchema;
+use serde::{Deserialize, Serialize};
+
 use crate::{
     AtlasTextureId, AtlasTile, Background, Bounds, ContentMask, Corners, Edges, Hsla, Pixels,
     Point, Radians, ScaledPixels, Size, bounds_tree::BoundsTree, point,
@@ -506,7 +509,7 @@ impl From<Shadow> for Primitive {
 }
 
 /// The style of a border.
-#[derive(Default, Debug, Clone, Copy, PartialEq, Eq, Hash)]
+#[derive(Default, Debug, Clone, Copy, PartialEq, Eq, Hash, Serialize, Deserialize, JsonSchema)]
 #[repr(C)]
 pub enum BorderStyle {
     /// A solid border.