[flash] Unbound variable with captured `inline extern` argument and `doc-gen`

```haxe
class Test {
  @:extern inline function foo(v) {
    return function() v;
  }
}
```

```hxml
Test
-D doc-gen
-swf main.swf
```

```haxe
[ERROR] Test.hx:3: characters 23-24

 3 |     return function() v;
   |                       ^
   | Unbound variable v
```

It also happens with haxe 3.4.7 so it's not a recent regression.