Re: [whatwg/encoding] Consider adding TextEncoder.containsLoneSurrogates() static (#174)

> To be clear, unpaired surrogates are invalid UTF-16, and so anything that generates them is (in my opinion) a bug.

JavaScript doesn't claim UTF-16 compatibility though, so it's not really a bug, but rather part of the language and so such strings should be taken into account in any APIs that interact with JS IMO (especially in encoders/decoders).

As mentioned above, I'm usually working with parsers in JavaScript. However, even without going into parsers that parse JavaScript itself, the simplest example can be created even with built-in `JSON.parse` API:

```js
> JSON.parse(String.raw`"\uD800"`)
"\ud800"
```

Here the input is perfectly valid UTF-8 / UTF-16, but the output is not, and has to be checked whether when passing string to WASM or encoding it to the disk, otherwise you're risking silent data loss that is not trivial to debug.

Hence my suggestion to enhance `TextEncoder` to check for lone surrogates automatically and throw the error before even crossing the boundary or losing the data.

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