Also, explicitly return text dimensions from text rasterization
functions. Older hardware requires texture image dimensions to be
powers of 2. Since the text will only be rendered into a portion of
the image in these cases, the text dimensions are needed to calculate
the texture coordinates during rendering.

Some classes were hiding the text dimensions in the image metadata, e.g.
texture coordinates and text dimensions were stored in Spacing and Origin.
This undocumented behavior was confusing and unintuitive.

Now functions that rendering scaled images explicitly return the text
dimensions.

Change-Id: Ic74b0dd9573d336427038985c671a8b724c92429