Fix a bug with invalid print output when empty array is passed to t.t…

…sInterfaceDeclaration

If you pass an empty array as `extends` in `t.tsInterfaceDeclaration` you'll get an invalid code printed

```ts
t.tsInterfaceDeclaration(
  t.identifier('x'),
  undefined,
  [],
  t.tsInterfaceBody([])
)
```

You will get
```ts
interface A extends {}
```

Which is an invalid TS, this PR fixes that

packages/babel-generator/src/generators/typescript.ts

@@ -435,7 +435,7 @@ export function TSInterfaceDeclaration(
   this.space();
   this.print(id, node);
   this.print(typeParameters, node);
-  if (extendz) {
+  if (extendz?.length) {
     this.space();
     this.word("extends");
     this.space();