syscall/js: copyBytesTo(Go|JS) could accept Uint8ClampedArray

When compiling Go to WebAssembly (with go 1.13) you can get a great help from syscall/js to interact with JS and web APIs.

One limitation is in reading and updating canvas pixel data with (get|put)ImageData, because we need an intermediary translation between Uint8ClampedArray and Uint8Array. Oderwise CopyBytesToGo panics, also we can't use a ImageData like object with Uint8Array data, or the putImageData will fail.

However, Uint8ClampedArray is just a sugary Uint8Array. I see no problem to make copyBytesTo(Go|JS) accepts that as a source or destiny.

What did you do?

// jsImgData = js.Value of Uint8ClampedArray
imgData := make([]uint8, jsImgData.Length())
// fill imgData with magic...
js.CopyBytesToJS(jsImgData, imgData)

What did you expect to see?

jsImgData filled to be puted in a canvas

What did you see instead?

The log syscall/js: CopyBytesToJS: expected dst to be an Uint8Array.