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/editor/src/editor.rs

@@ -1539,6 +1539,7 @@ pub(crate) struct NavigationData {
 
 enum GotoDefinitionKind {
     Symbol,
+    Declaration,
     Type,
     Implementation,
 }
@@ -8948,6 +8949,22 @@ impl Editor {
         self.go_to_definition_of_kind(GotoDefinitionKind::Symbol, false, cx)
     }
 
+    pub fn go_to_declaration(
+        &mut self,
+        _: &GoToDeclaration,
+        cx: &mut ViewContext<Self>,
+    ) -> Task<Result<bool>> {
+        self.go_to_definition_of_kind(GotoDefinitionKind::Declaration, false, cx)
+    }
+
+    pub fn go_to_declaration_split(
+        &mut self,
+        _: &GoToDeclaration,
+        cx: &mut ViewContext<Self>,
+    ) -> Task<Result<bool>> {
+        self.go_to_definition_of_kind(GotoDefinitionKind::Declaration, true, cx)
+    }
+
     pub fn go_to_implementation(
         &mut self,
         _: &GoToImplementation,
@@ -9008,6 +9025,7 @@ impl Editor {
         let project = workspace.read(cx).project().clone();
         let definitions = project.update(cx, |project, cx| match kind {
             GotoDefinitionKind::Symbol => project.definition(&buffer, head, cx),
+            GotoDefinitionKind::Declaration => project.declaration(&buffer, head, cx),
             GotoDefinitionKind::Type => project.type_definition(&buffer, head, cx),
             GotoDefinitionKind::Implementation => project.implementation(&buffer, head, cx),
         });