Formalize type declarations/annotations for shape objects for rendering.

[rachel-fenichel]

Objects like Blockly.blockRendering.constants.PUZZLE_TAB are used for rendering now, and should be swappable as long as we have a good description of what properties each one needs to have. Right now that's lacking.

Here is a sample object:

Blockly.blockRendering.constants.NOTCH = (function() {
  var width = Blockly.blockRendering.constants.NOTCH_WIDTH;
  var height = Blockly.blockRendering.constants.NOTCH_HEIGHT;
  var innerWidth = 3;
  var outerWidth = (width - innerWidth) / 2;
  function makeMainPath(dir) {
    return Blockly.utils.svgPaths.line(
        [
          Blockly.utils.svgPaths.point(dir * outerWidth, height),
          Blockly.utils.svgPaths.point(dir * innerWidth, 0),
          Blockly.utils.svgPaths.point(dir * outerWidth, -height)
        ]);
  }
  // TODO: Find a relationship between width and path
  var pathLeft = makeMainPath(1);
  var pathRight = makeMainPath(-1);

  return {
    width: width,
    height: height,
    pathLeft: pathLeft,
    pathRight: pathRight
  };
})();

Notice that it evaluates immediately, so the actual object just has width, height, pathLeft, and pathRight properties for the rest of the rendering code to use.

[rachel-fenichel]

Additional note from the rendering hackathon: some shape objects call makeMainPath with -1 or 1, while others use true or false.

We should be consistent.