Effects: Use FullScreenQuad.

[Mugen87]

Related issue: -

Description

AnaglyphEffect and ParallaxBarrierEffect can make use of FullScreenQuad which simplifies the code a bit.

Besides, the PR adds the missing dispose() method to ParallaxBarrierEffect.

[Mugen87]

BTW: I think we can port StereoEffect, AnaglyphEffect and ParallaxBarrierEffect as StereoPassNode, AnaglyphPassNode and ParallaxBarrierPassNode in nodes/display. They would be used via PostProcessing like so:

postProcessing = new THREE.PostProcessing( renderer );

const stereoScenePass = stereoPass( scene, camera );
// const anaglyphScenePass = anaglyphPass( scene, camera );
// const parallaxBarrierScenePass = parallaxBarrierPass( scene, camera );

postProcessing.outputNode = stereoScenePass;

[mrdoob]

BTW: I think we can port StereoEffect, AnaglyphEffect and ParallaxBarrierEffect as StereoPassNode, AnaglyphPassNode and ParallaxBarrierPassNode in nodes/display.

Agreed! And would be great to remove these files eventually.