shadow: rework on stroke and fill inset shadow

Simply fill and stroke inset shadow.  For inset shadow, we first fill
or stroke the original source.  Then we create an inset shadow using
shadow color and paint the created inset shadow on top of source
shadow: rework on inset shadow text rendering
image: modify image surface to support inset shadow
xcb: rework on shadow for fill, stroke and glyphs

we draw original image first, then apply the inset shadow.  For drop
shadow, we reverse the order, we draw drop shadow first, then the original
image