The new function js.TypedArrayOf returns a JavaScript typed array for
a given slice.
https://developer.mozilla.org/en-US/docs/Web/JavaScript/Typed_arrays

This change also changes js.ValueOf to not accept a []byte any more.

Fixes #25532.

Change-Id: I8c7bc98ca4e21c3514d19eee7a1f92388d74ab2a
Reviewed-on: https://go-review.googlesource.com/121215
Run-TryBot: Brad Fitzpatrick <bradfitz@golang.org>
TryBot-Result: Gobot Gobot <gobot@golang.org>
Reviewed-by: Brad Fitzpatrick <bradfitz@golang.org>