Rewrite rendering engine (#6253)

* Clean draw_*() arguments

* Split rendering core

* Add anaglyph 3D

* Interlaced 3D

* Drop obsolete methods

minetest.conf.example

@@ -700,6 +700,7 @@
 #    -    topbottom: split screen top/bottom.
 #    -    sidebyside: split screen side by side.
 #    -    pageflip: quadbuffer based 3d.
+#    Note that the interlaced mode requires shaders to be enabled.
 #    type: enum values: none, anaglyph, interlaced, topbottom, sidebyside, pageflip
 # 3d_mode = none