The Graph Editor keyframe dots (and handles) are currently scaled with U.pixelsize. This means (at default size) those dots start at 6 pixels wide at 1X interface scale and then jump immediately to 12 pixels at 1.8 scale. And immediately to 18 at 2.8 scale.

This patch changes this so that they are scaled smoothly with U.dpi_fac. This way they will be 6 pixels at 1X, 9 pixels at 1.5, 12 pixels at 2x, etc. And with all sizes in between.

Sometimes it is nice to include U.pixelsize in the scaling calculation, since when done right a user can have a small scale but larger features by selecting "wide lines". But that does not apply here since we have independent theme selection of dot and handle sizes. So users can select any size they like. But then they should be scaled by U.dpi_fac.