Refactor helpers.canvas.drawPoint() (#5623)

Bring ctx.beginPath() before switch and replace ctx.fillRect()/ctx.strokeRect() with ctx.rect()/ctx.fill() to make it consistent with the other styles. It is also preferable that helpers.canvas.roundedRect() include ctx.closePath() at the end because CanvasRenderingContext2D.rect() closes the subpath.

Get rid of ctx.closePath() for cross, crossRot, star, line and dash because these have no closed path shape, and it should be avoided that ctx.closePath() makes a round-trip path.