cogl-shader-boilerplate: Add the 3D texture extension on GLES2
cogl-shader-boilerplate: Add the 3D texture extension on GLES2

To use the 3D texture extension on GLES2 it has to be enabled with the
following line in GLSL:

#extension GL_OES_texture_3D : enable

collects/clutter,jigpu/clutter,jigpu/clutter,GNOME/clutter,djdeath/clutter,djdeath/clutter,GNOME/clutter,djdeath/clutter-android,Distrotech/clutter,ebassi/clutter,Distrotech/clutter,djdeath/clutter-multithreaded,ebassi/clutter,heysion/clutter-clone,jigpu/clutter,dlespiau/clutter,djdeath/clutter-android,ebassi/clutter,Distrotech/clutter,djdeath/clutter-android,Distrotech/clutter,nobled/clutter,GNOME/clutter,heysion/clutter-clone,kerrickstaley/clutter-vala,nobled/clutter,collects/clutter,djdeath/clutter-android,heysion/clutter-clone,dlespiau/clutter,ebassi/clutter,spatulasnout/clutter,spatulasnout/clutter,spatulasnout/clutter,heysion/clutter-clone,spatulasnout/clutter,djdeath/clutter-multithreaded,djdeath/clutter,djdeath/clutter-multithreaded,ebassi/clutter,heysion/clutter-clone,collects/clutter,jigpu/clutter,Distrotech/clutter,GNOME/clutter,djdeath/clutter-android,djdeath/clutter,kerrickstaley/clutter-vala,Distrotech/clutter,jigpu/clutter,collects/clutter,djdeath/clutter,collects/clutter,kerrickstaley/clutter-vala,dlespiau/clutter,GNOME/clutter,kerrickstaley/clutter-vala,spatulasnout/clutter,djdeath/clutter-multithreaded,nobled/clutter,jigpu/clutter,djdeath/clutter