Add a live Rust style editor to inspector to edit a sequence of no-argument style modifiers (#31443)

Editing JSON styles is not very helpful for bringing style changes back
to the actual code. This PR adds a buffer that pretends to be Rust,
applying any style attribute identifiers it finds. Also supports
completions with display of documentation. The effect of the currently
selected completion is previewed. Warning diagnostics appear on any
unrecognized identifier.


https://github.com/user-attachments/assets/af39ff0a-26a5-4835-a052-d8f642b2080c

Adds a `#[derive_inspector_reflection]` macro which allows these methods
to be enumerated and called by their name. The macro code changes were
95% generated by Zed Agent + Opus 4.

Release Notes:

* Added an element inspector for development. On debug builds,
`dev::ToggleInspector` will open a pane allowing inspecting of element
info and modifying styles.

crates/gpui_macros/src/gpui_macros.rs

@@ -6,6 +6,9 @@ mod register_action;
 mod styles;
 mod test;
 
+#[cfg(any(feature = "inspector", debug_assertions))]
+mod derive_inspector_reflection;
+
 use proc_macro::TokenStream;
 use syn::{DeriveInput, Ident};
 
@@ -178,6 +181,28 @@ pub fn test(args: TokenStream, function: TokenStream) -> TokenStream {
     test::test(args, function)
 }
 
+/// When added to a trait, `#[derive_inspector_reflection]` generates a module which provides
+/// enumeration and lookup by name of all methods that have the shape `fn method(self) -> Self`.
+/// This is used by the inspector so that it can use the builder methods in `Styled` and
+/// `StyledExt`.
+///
+/// The generated module will have the name `<snake_case_trait_name>_reflection` and contain the
+/// following functions:
+///
+/// ```ignore
+/// pub fn methods::<T: TheTrait + 'static>() -> Vec<gpui::inspector_reflection::FunctionReflection<T>>;
+///
+/// pub fn find_method::<T: TheTrait + 'static>() -> Option<gpui::inspector_reflection::FunctionReflection<T>>;
+/// ```
+///
+/// The `invoke` method on `FunctionReflection` will run the method. `FunctionReflection` also
+/// provides the method's documentation.
+#[cfg(any(feature = "inspector", debug_assertions))]
+#[proc_macro_attribute]
+pub fn derive_inspector_reflection(_args: TokenStream, input: TokenStream) -> TokenStream {
+    derive_inspector_reflection::derive_inspector_reflection(_args, input)
+}
+
 pub(crate) fn get_simple_attribute_field(ast: &DeriveInput, name: &'static str) -> Option<Ident> {
     match &ast.data {
         syn::Data::Struct(data_struct) => data_struct