lsp: Complete overloaded signature help implementation (#33199)

This PR revives zed-industries/zed#27818 and aims to complete the
partially implemented overloaded signature help feature.

The first commit is a rebase of zed-industries/zed#27818, and the
subsequent commit addresses all review feedback from the original PR.

Now the overloaded signature help works like


https://github.com/user-attachments/assets/e253c9a0-e3a5-4bfe-8003-eb75de41f672

Closes #21493

Release Notes:

- Implemented signature help for overloaded items. Additionally, added a
support for rendering signature help documentation.

---------

Co-authored-by: Fernando Tagawa <tagawafernando@gmail.com>
Co-authored-by: Claude <noreply@anthropic.com>
Co-authored-by: Kirill Bulatov <mail4score@gmail.com>
Co-authored-by: Kirill Bulatov <kirill@zed.dev>

crates/theme/src/styles/accents.rs

@@ -7,7 +7,7 @@ use crate::{
 };
 
 /// A collection of colors that are used to color indent aware lines in the editor.
-#[derive(Clone, Deserialize, PartialEq)]
+#[derive(Clone, Debug, Deserialize, PartialEq)]
 pub struct AccentColors(pub Vec<Hsla>);
 
 impl Default for AccentColors {

crates/theme/src/styles/colors.rs

@@ -535,7 +535,7 @@ pub fn all_theme_colors(cx: &mut App) -> Vec<(Hsla, SharedString)> {
         .collect()
 }
 
-#[derive(Refineable, Clone, PartialEq)]
+#[derive(Refineable, Clone, Debug, PartialEq)]
 pub struct ThemeStyles {
     /// The background appearance of the window.
     pub window_background_appearance: WindowBackgroundAppearance,

crates/theme/src/styles/players.rs

@@ -20,7 +20,7 @@ pub struct PlayerColor {
 ///
 /// The rest of the default colors crisscross back and forth on the
 /// color wheel so that the colors are as distinct as possible.
-#[derive(Clone, Deserialize, PartialEq)]
+#[derive(Clone, Debug, Deserialize, PartialEq)]
 pub struct PlayerColors(pub Vec<PlayerColor>);
 
 impl Default for PlayerColors {

crates/theme/src/styles/system.rs

@@ -2,7 +2,7 @@
 
 use gpui::{Hsla, hsla};
 
-#[derive(Clone, PartialEq)]
+#[derive(Clone, Debug, PartialEq)]
 pub struct SystemColors {
     pub transparent: Hsla,
     pub mac_os_traffic_light_red: Hsla,

crates/theme/src/theme.rs

@@ -268,7 +268,7 @@ pub fn refine_theme_family(theme_family_content: ThemeFamilyContent) -> ThemeFam
 }
 
 /// A theme is the primary mechanism for defining the appearance of the UI.
-#[derive(Clone, PartialEq)]
+#[derive(Clone, Debug, PartialEq)]
 pub struct Theme {
     /// The unique identifier for the theme.
     pub id: String,