vm2: Sandboxed code can read and write host-realm memory via Node's shared Buffer pool

### Summary Sandboxed code is able to disclose host memory used by small allocations by `Buffer.from`, `Buffer.concat`. ### Details vm2 exposes `Buffer` object to sandboxed code by default. Small [`Buffer` allocations](https://nodejs.org/api/buffer.html#static-method-bufferallocunsafesize) (for example, [Buffer.allocUnsafe()](https://nodejs.org/api/buffer.html#static-method-bufferallocunsafesize), [Buffer.from(array)](https://nodejs.org/api/buffer.html#static-method-bufferfromarray), [Buffer.from(string)](https://nodejs.org/api/buffer.html#static-method-bufferfromstring-encoding), and [Buffer.concat()](https://nodejs.org/api/buffer.html#static-method-bufferconcatlist-totallength)) use the same Buffer pool, which is shared with the sandbox. This allows sandboxed code to disclose host memory used by the functions listed above. ### PoC Tested against `vm2@3.11.5` in the node REPL. ```javascript Buffer.from('host-memory-should-not-leak-to-sandbox') new (require('vm2').VM)().run(`Buffer.from(Buffer.from([0]).buffer, 0, Buffer.from([0]).buffer.byteLength).toString('ascii')`) ``` ### Impact Since sandbox acquires an ArrayBuffer that is used by the host, it can disclose sensitive data going through functions mentioned above and even write to these buffers, which can lead to sensitive data exposure and potentially denial-of-service.