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/mouse_context_menu.rs

@@ -1,5 +1,6 @@
 use std::ops::Range;
 
+use crate::GoToDeclaration;
 use crate::{
     selections_collection::SelectionsCollection, Copy, CopyPermalinkToLine, Cut, DisplayPoint,
     DisplaySnapshot, Editor, EditorMode, FindAllReferences, GoToDefinition, GoToImplementation,
@@ -163,6 +164,7 @@ pub fn deploy_context_menu(
                 .on_blur_subscription(Subscription::new(|| {}))
                 .action("Rename Symbol", Box::new(Rename))
                 .action("Go to Definition", Box::new(GoToDefinition))
+                .action("Go to Declaration", Box::new(GoToDeclaration))
                 .action("Go to Type Definition", Box::new(GoToTypeDefinition))
                 .action("Go to Implementation", Box::new(GoToImplementation))
                 .action("Find All References", Box::new(FindAllReferences))