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/styled.rs

@@ -1,18 +1,16 @@
 use crate::{
-    self as gpui, AbsoluteLength, AlignItems, BorderStyle, CursorStyle, DefiniteLength, Fill,
-    FlexDirection, FlexWrap, Font, FontStyle, FontWeight, Hsla, JustifyContent, Length,
-    SharedString, StrikethroughStyle, StyleRefinement, TextOverflow, UnderlineStyle, WhiteSpace,
-    px, relative, rems,
+    self as gpui, AbsoluteLength, AlignContent, AlignItems, BorderStyle, CursorStyle,
+    DefiniteLength, Display, Fill, FlexDirection, FlexWrap, Font, FontStyle, FontWeight, Hsla,
+    JustifyContent, Length, SharedString, StrikethroughStyle, StyleRefinement, TextAlign,
+    TextOverflow, TextStyleRefinement, UnderlineStyle, WhiteSpace, px, relative, rems,
 };
-use crate::{TextAlign, TextStyleRefinement};
 pub use gpui_macros::{
     border_style_methods, box_shadow_style_methods, cursor_style_methods, margin_style_methods,
     overflow_style_methods, padding_style_methods, position_style_methods,
     visibility_style_methods,
 };
-use taffy::style::{AlignContent, Display};
 
-const ELLIPSIS: &str = "…";
+const ELLIPSIS: SharedString = SharedString::new_static("…");
 
 /// A trait for elements that can be styled.
 /// Use this to opt-in to a utility CSS-like styling API.
@@ -67,7 +65,7 @@ pub trait Styled: Sized {
     fn text_ellipsis(mut self) -> Self {
         self.text_style()
             .get_or_insert_with(Default::default)
-            .text_overflow = Some(TextOverflow::Ellipsis(ELLIPSIS));
+            .text_overflow = Some(TextOverflow::Truncate(ELLIPSIS));
         self
     }