Annotate Collections.toArray() methods

Annotate Collections.toArray() methods

Both variants return @NonNull array references. The one with the
(T[]) parameter can also e annotated to require a @NonNull array
reference (or else it would just throw an NPE).

Note this covers only the array references themselves. The
contained element types will depend on what is passed in parameter

Change-Id: I31bed98a0b7d1df3486179a9e60cb8c73eb0038d
Signed-off-by: Alexandre Montplaisir <alexmonthy@voxpopuli.im>
Reviewed-on: https://git.eclipse.org/r/59421
Reviewed-by: Hudson CI
Reviewed-by: Marc-Andre Laperle <marc-andre.laperle@ericsson.com>
Tested-by: Marc-Andre Laperle <marc-andre.laperle@ericsson.com>