Add vscode support for range in SyntaxTreeParams

This enables the client to use a command to either show the live-updating
version of the syntax tree for the current file. Or optionally when a selected
range is provided, we then provide a snapshot of the syntax tree for the range.

editors/code/src/extension.ts

@@ -52,7 +52,6 @@ export function activate(context: vscode.ExtensionContext) {
     registerCommand('rust-analyzer.collectGarbage', () =>
         Server.client.sendRequest<null>('rust-analyzer/collectGarbage', null)
     );
-    registerCommand('rust-analyzer.syntaxTree', commands.syntaxTree.handle);
     registerCommand(
         'rust-analyzer.extendSelection',
         commands.extendSelection.handle
@@ -109,6 +108,11 @@ export function activate(context: vscode.ExtensionContext) {
         )
     );
 
+    registerCommand(
+        'rust-analyzer.syntaxTree',
+        commands.syntaxTree.createHandle(textDocumentContentProvider)
+    );
+
     vscode.workspace.onDidChangeTextDocument(
         events.changeTextDocument.createHandler(textDocumentContentProvider),
         null,