Allow ArrayBuffer in uint8ArrayToString() or add a similar method

[sholladay]

I naively replaced new TextDecoder(data).decode() with uint8ArrayToString(data), in hopes of making use of the decoder cache and keeping my code concise and consistent (i.e. always use the library's decoder or always my own, not mix and match).

However, I immediately ran into an error:

error: Uncaught (in promise) TypeError: Expected `Uint8Array`, got `object

This was caused by the fact that data was not a Uint8Array but rather an ArrayBuffer, as returned by the Web Crypto API encrypt() / decrypt() methods.

Given the function name, I suppose I should've anticipated this, but because TextDecoder handles ArrayBuffers, I thought it would be fine.

How necessary is the assertion in that function? Maybe there could be a new method or option for bypassing that assertion?