Layoutlib: add support for ITextServicesManager.

This include a fix in layoutlib_create to properly handle
delegating a static method of an inner class (was broken and
only worked on non static method).

Added a few comments here and there to *_Accessor classes so
that it's a bit more obvious what they are for and how they are
used.

Change-Id: Ifc31dd1a006393bb0c08e22b6a17f500dd62e090