Minor fixes to android.opengl.Matrix

This has a minor API change: deprecation of the nullary constructor.
The class is entirely composed of static methods, and was written
without a constructor, but the compiler dutifully generated a
default implementation and the API tool slurped it up.

The other changes are to the documentation:

 - Added warnings about the use of overlapping input and output
   on certain methods.
 - Fixed a few inaccuracies (e.g. transposeM() returns a transposed
   matrix, not an inverted matrix).
 - Tidied up the formatting.
 - Generally placated the consistency hobgoblins.

Bug 8868762

Change-Id: Ie3f86b98c477d8dc82d9dcaa311959bd4d191359