Implement some advance blending equation in GLEngine by using two
RenderPass.
* The first pass render the content into an off-screen framebuffer, also
blit the screen content to an off-screen Texture.
* The second pass renders the final blended color to the screen.
Also use a stencil test to prevent non-drawn areas from participating in the color blending calculation.
issue: https://github.com/thorvg/thorvg/issues/2435
Since blit msaa framebuffer to another msaa framebuffer may generate
GLError in some platforms. Use normal texture rendering to blit the final
color buffer onto target framebuffer.
* add new render task to do stencil and cover rendering which is a
fallback rendering method to handle cases that trianglation tessellation
failed
* add a new tessellator to generate stencil and cover vertex mesh
