Target both reading and writing on the framebuffer with glBindFramebuffer

Property definitions

glesv2 :: glesv2 $ Sys :: gl_FRAMEBUFFER
# Target both reading and writing on the framebuffer with `glBindFramebuffer`
fun gl_FRAMEBUFFER: GLFramebufferTarget `{ return GL_FRAMEBUFFER; `}
lib/glesv2/glesv2.nit:891,1--892,68