Show color swatches for LSP completions (#18665)

Closes #11991

Release Notes:

- Added support for color swatches for language server completions.

<img width="502" alt="Screenshot 2024-10-02 at 19 02 22"
src="https://github.com/user-attachments/assets/57e85492-3760-461a-9b17-a846dc40576b">

<img width="534" alt="Screenshot 2024-10-02 at 19 02 48"
src="https://github.com/user-attachments/assets/713ac41c-16f0-4ad3-9103-d2c9b3fa8b2e">

This implementation is mostly a port of the VSCode version of the
ColorExtractor. It seems reasonable the we should support _at least_
what VSCode does for detecting color swatches from LSP completions.

This implementation could definitely be better perf-wise by writing a
dedicated color parser. I also think it would be neat if, in the future,
Zed handled _more_ color formats — especially wide-gamut colors.

There are a few differences to the regexes in the VSCode implementation
but mainly so simplify the implementation :
- The hex vs rgb/hsl regexes were split into two parts
- The rgb/hsl regexes allow 3 or 4 color components whether hsla/rgba or
not and the parsing implementation accepts/rejects colors as needed

---------

Co-authored-by: Marshall Bowers <elliott.codes@gmail.com>

crates/project/src/project.rs

@@ -1,4 +1,5 @@
 pub mod buffer_store;
+mod color_extractor;
 pub mod connection_manager;
 pub mod debounced_delay;
 pub mod lsp_command;
@@ -36,7 +37,7 @@ use futures::{
 
 use git::{blame::Blame, repository::GitRepository};
 use gpui::{
-    AnyModel, AppContext, AsyncAppContext, BorrowAppContext, Context, EventEmitter, Model,
+    AnyModel, AppContext, AsyncAppContext, BorrowAppContext, Context, EventEmitter, Hsla, Model,
     ModelContext, SharedString, Task, WeakModel, WindowContext,
 };
 use itertools::Itertools;
@@ -47,7 +48,9 @@ use language::{
     Documentation, File as _, Language, LanguageRegistry, LanguageServerName, PointUtf16, ToOffset,
     ToPointUtf16, Transaction, Unclipped,
 };
-use lsp::{CompletionContext, DocumentHighlightKind, LanguageServer, LanguageServerId};
+use lsp::{
+    CompletionContext, CompletionItemKind, DocumentHighlightKind, LanguageServer, LanguageServerId,
+};
 use lsp_command::*;
 use node_runtime::NodeRuntime;
 use parking_lot::{Mutex, RwLock};
@@ -4445,6 +4448,16 @@ impl Completion {
     pub fn is_snippet(&self) -> bool {
         self.lsp_completion.insert_text_format == Some(lsp::InsertTextFormat::SNIPPET)
     }
+
+    /// Returns the corresponding color for this completion.
+    ///
+    /// Will return `None` if this completion's kind is not [`CompletionItemKind::COLOR`].
+    pub fn color(&self) -> Option<Hsla> {
+        match self.lsp_completion.kind {
+            Some(CompletionItemKind::COLOR) => color_extractor::extract_color(&self.lsp_completion),
+            _ => None,
+        }
+    }
 }
 
 #[derive(Debug)]