Add a CrossProcessCursorWrapper.

Bug: 5220669

The CrossProcessCursorWrapper is a useful building block
for wrapping cursors that will be sent to processes remotely.
It can also transform normal Cursors into CrossProcessCursors
transparently.

The new class fixes common performance problems and bugs
that applications have encountered when implementing
ContentProviders.

Change-Id: Icc59fec10add3f7d8cfbd0495447860c1872c752