Fix bounds checks, etc. in ArrayDeque

[szeiger]

This also affects subclasses like mutable.Queue.

• Remove unnecessary from paramter in requireBounds.
• Allow copyToSlice directly beyond the end of a target array for a no-op. This is required to make it work for empty arrays.
• Allow insert and insertAll directly beyond the end of the ArrayDeque for appending to the end.
• Remove explicit className in ArrayDeque to have it computed correctly for subclasses like Queue.

Fixes https://github.com/scala/collection-strawman/issues/506