Handle block comments

Longer values require multi-line print, so we need to handle the block comments
For example
```js
const v = {foo: {bar: 'baz'}}
/* v: */
```
should expand into
```js
const v = {foo: {bar: 'baz'}}
/* v: {
foo: {
bar: 'baz'
}
}
*/
```

No file or test is named in the issue. Start by reproducing the JavaScript example and locating the instrumentation entry point that handles the existing /* v: */ form; done means a nested object is expanded into the requested multi-line block comment without breaking the surrounding source.

Written by the indexing model from the issue text.