Improve Blurry Texture Rendering in WebGLRenderer

[jonobr1]

Reported by @benz2012:

• https://github.com/jonobr1/two.js/issues/703

This PR improves blurry textures by appropriately scaling uploaded textures to the GPU by the renderer's pixel density.

Before	After

For a scene such as:

const two = new Two({
  type: Two.Types.webgl,
  fullscreen: true,
  autostart: true
}).appendTo(document.body);

const params = {
  size: 100,
  fill: '#000',
  stroke: '#00aeff',
  linewidth: 3,
  weight: 'bold'
};
const text = two.makeText('Hello World', two.width / 2, two.height / 2, params);