lsp: Support Goto Declaration (#15785)

Adds support for [Goto
Declaration](https://microsoft.github.io/language-server-protocol/specifications/lsp/3.17/specification/#textDocument_declaration)
LSP command.

I am particularly interested in [this for Rust
projects](https://rust-analyzer.github.io/manual.html#go-to-declaration),
to be able to navigate to the place where a trait method is declared,
coming from a trait method implementation.

I noticed this was something I could do in VSCode before, but was
somehow missing is Zed. Thanks to the already existing infrastructure
for Goto Definition, I just followed and copy-paste-adapted it for Goto
Declaration.

As a bonus, I added `ctrl-F12` and `alt-ctrl-F12` as default macOS
keybindings for `GoToDeclaration` and `GoToDeclarationSplit`,
respectively. They are not keybindings from another editor, but I
figured they made sense to be grouped along with the other *F12
commands.

### Release Notes:

- Added "Go to declaration" editor action.
- vim: Breaking change to keybindings after introduction of the `Go to
declaration` editor action. The new keybindings are the following (and
can be found [here](https://zed.dev/docs/vim), alongside the other key
bindings):
  - `g d` - Go to definition
  - `g D` - Go to declaration
  - `g y` - Go to type definition
  - `g I` - Go to implementation




https://github.com/user-attachments/assets/ee5c10a8-94f0-4e50-afbb-6f71db540c1b

---------

Co-authored-by: Thorsten Ball <mrnugget@gmail.com>

crates/project/src/project.rs

@@ -714,6 +714,7 @@ impl Project {
         client.add_model_request_handler(Self::handle_lsp_command::<GetCompletions>);
         client.add_model_request_handler(Self::handle_lsp_command::<GetHover>);
         client.add_model_request_handler(Self::handle_lsp_command::<GetDefinition>);
+        client.add_model_request_handler(Self::handle_lsp_command::<GetDeclaration>);
         client.add_model_request_handler(Self::handle_lsp_command::<GetTypeDefinition>);
         client.add_model_request_handler(Self::handle_lsp_command::<GetDocumentHighlights>);
         client.add_model_request_handler(Self::handle_lsp_command::<GetReferences>);
@@ -5463,6 +5464,30 @@ impl Project {
         self.definition_impl(buffer, position, cx)
     }
 
+    fn declaration_impl(
+        &self,
+        buffer: &Model<Buffer>,
+        position: PointUtf16,
+        cx: &mut ModelContext<Self>,
+    ) -> Task<Result<Vec<LocationLink>>> {
+        self.request_lsp(
+            buffer.clone(),
+            LanguageServerToQuery::Primary,
+            GetDeclaration { position },
+            cx,
+        )
+    }
+
+    pub fn declaration<T: ToPointUtf16>(
+        &self,
+        buffer: &Model<Buffer>,
+        position: T,
+        cx: &mut ModelContext<Self>,
+    ) -> Task<Result<Vec<LocationLink>>> {
+        let position = position.to_point_utf16(buffer.read(cx));
+        self.declaration_impl(buffer, position, cx)
+    }
+
     fn type_definition_impl(
         &self,
         buffer: &Model<Buffer>,