Modify Canvas drawText to run bidi and shape.

Adds drawTextRun as internal API on Canvas and GraphicsOperations.
Adds implementation to implementors of GraphicsOperations.

Adds state and API on Paint to control the bidi algorithm when used
by Canvas.  This API is currently hidden.

The drawText changes are incomplete since shaping is not yet available
in the native code.

Change-Id: I4368048aef9545df0953a349381771603e04b619