Before this change, texture atlases are created only for rendreing
sources.
This change enables to use texture atlases even for rendering
destinations, so that the number of textures will be drastically
reduced.
Closes#2581
Adjusting pixels is needed to avoid strainge rendering to avoid unexpected
rendering (#1171). However, this adjustment caused unexpected holes
especially in a thick stroke.
This change moves the logic of adjusting pixels from atlas to
graphics.QuadVertices so that adjusting works only for DrawImage and
DrawRectShader.
Updates #1171
Updates #1843
