Add language(s) hint to TextDetector's detect function

OCR libraries like [Tesseract](https://github.com/tesseract-ocr/tesseract/wiki/Command-Line-Usage#tesseract---help) tend to work better if the input language is known. I would thus suggest to add a language(s) hint option to the [`detect`](https://wicg.github.io/shape-detection-api/text.html#dom-textdetector-detect) function of the `TextDetector`.