automate braceless return substitution for long lines

Per [bjorn3][https://github.com/bjorn3] suggestion resolves cases where
an early return is moved to a separate line due to line width formatting.

This setting changes
```
if (a very long condition) return;
```
to
```
if (a very long
    condition) {
  return;
}
```
while keeping
```
if (short) return;
```
as is.

In pathological cases this may cause `npm run fix` not to fix formatting
in one go and may require running it twice.

editors/code/.eslintrc.js

@@ -14,6 +14,7 @@ module.exports = {
     rules: {
         camelcase: ["error"],
         eqeqeq: ["error", "always", { null: "ignore" }],
+        curly: ["error", "multi-line"],
         "no-console": ["error", { allow: ["warn", "error"] }],
         "prefer-const": "error",
         "@typescript-eslint/member-delimiter-style": [

editors/code/src/ast_inspector.ts

@@ -101,8 +101,9 @@ export class AstInspector implements vscode.HoverProvider, vscode.DefinitionProv
         doc: vscode.TextDocument,
         pos: vscode.Position
     ): vscode.ProviderResult<vscode.DefinitionLink[]> {
-        if (!this.rustEditor || doc.uri.toString() !== this.rustEditor.document.uri.toString())
+        if (!this.rustEditor || doc.uri.toString() !== this.rustEditor.document.uri.toString()) {
             return;
+        }
 
         const astEditor = this.findAstTextEditor();
         if (!astEditor) return;

editors/code/src/snippets.ts

@@ -11,7 +11,7 @@ export async function applySnippetWorkspaceEdit(edit: vscode.WorkspaceEdit) {
     }
     for (const [uri, edits] of edit.entries()) {
         const editor = await editorFromUri(uri);
-        if (editor)
+        if (editor) {
             await editor.edit((builder) => {
                 for (const indel of edits) {
                     assert(
@@ -21,6 +21,7 @@ export async function applySnippetWorkspaceEdit(edit: vscode.WorkspaceEdit) {
                     builder.replace(indel.range, indel.newText);
                 }
             });
+        }
     }
 }