Improve detection of transferring array buffers.

Remove `FeatureDetection.supportsTransferringArrayBuffers` which incorrectly used `window.postMessage`.  Fixes #1571.

Detection is now done internally inside `TaskProcessor` using a real web worker, which round-trips a typed array to detect a related bug in older Firefox versions.  `TaskProcessor` sends the result of the detection to the worker along with the task object, instead of having the worker detect itself.

Instead of detecting whether or not `ArrayBuffers` can be transferred everywhere in Cesium code, we now assume they can, and the `TaskProcessor`/`createTaskProcessorWorker` system will internally truncate the array if it's not supported.

Fixes #1598 by removing the need for `stupefyTypedArray` entirely.