Issue #4336: WebGLRenderer: Consistent application of devicePixelRatio to parameters of setSize, setViewport and setScissor

Changes to WebGLRenderer.setSize, setViewport and setScissor and a recent change to examples/webgl_multiple_views.html had to be reverted.

Not sure about the new default values in setScissor.

An additional change to WebGLRenderer.setRenderTarget might be necessary.