lsp: Update root_path for compatibility with language servers (#48587)

This PR updates the deprecated `rootPath` field in the LSP
`InitializeParams` for backwards compatibility with language servers
that still rely on this field.

### Issue

Some language servers (notably the Salesforce Apex Language Server) only
read from the deprecated `rootPath` field in the LSP initialize request
and do not use `rootUri` or `workspaceFolders`.

When Zed sends `root_path: None`, these language servers fail to
initialize because they cannot determine the workspace root.

Example error from the Apex Language Server:
```
NullPointerException
  at apex.jorje.lsp.impl.db.nddb.NdApexIndex.getToolsStoragePath(NdApexIndex.java:723)
```

The Apex LSP's initialize handler does:
```java
serverSetup.setRootPath(params.getRootPath());
```

VSCode's LanguageClient sends both `rootPath` and `rootUri` for
backwards compatibility:

https://github.com/microsoft/vscode-languageserver-node/blob/main/client/src/common/client.ts#L1434

### Fix

Derive `rootPath` from the existing `root_uri` field when building the
initialize params. The LSP spec states that if both `rootPath` and
`rootUri` are provided, `rootUri` wins, so this change should be
backwards compatible and won't affect language servers that properly use
`rootUri`<sup>(1)</sup>.


---

(1) [LSP Specification -
InitializeParams](https://microsoft.github.io/language-server-protocol/specifications/lsp/3.17/specification/#initializeParams)
- notes that `rootPath` is deprecated in favor of `workspaceFolders`,
but for backwards compatibility it should still be provided when
possible.


Release Notes:

- Improved compatibility with legacy language servers

crates/lsp/src/lsp.rs

@@ -738,7 +738,12 @@ impl LanguageServer {
         #[allow(deprecated)]
         InitializeParams {
             process_id: Some(std::process::id()),
-            root_path: None,
+            root_path: Some(
+                self.root_uri
+                    .to_file_path()
+                    .map(|path| path.to_string_lossy().into_owned())
+                    .unwrap_or_else(|_| self.root_uri.path().to_string()),
+            ),
             root_uri: Some(self.root_uri.clone()),
             initialization_options: None,
             capabilities: ClientCapabilities {
@@ -2104,4 +2109,38 @@ mod tests {
             "{\"jsonrpc\":\"\",\"id\":0,\"error\":null}"
         );
     }
+
+    #[gpui::test]
+    async fn test_initialize_params_has_root_path_and_root_uri(cx: &mut TestAppContext) {
+        cx.update(|cx| {
+            release_channel::init(semver::Version::new(0, 0, 0), cx);
+        });
+        let (server, _fake) = FakeLanguageServer::new(
+            LanguageServerId(0),
+            LanguageServerBinary {
+                path: "path/to/language-server".into(),
+                arguments: vec![],
+                env: None,
+            },
+            "test-lsp".to_string(),
+            Default::default(),
+            &mut cx.to_async(),
+        );
+
+        let params = cx.update(|cx| server.default_initialize_params(false, false, cx));
+
+        #[allow(deprecated)]
+        let root_uri = params.root_uri.expect("root_uri should be set");
+        #[allow(deprecated)]
+        let root_path = params.root_path.expect("root_path should be set");
+
+        let expected_path = root_uri
+            .to_file_path()
+            .expect("root_uri should be a valid file path");
+        assert_eq!(
+            root_path,
+            expected_path.to_string_lossy(),
+            "root_path should be derived from root_uri"
+        );
+    }
 }