[macOS] Wrong calculation of slider's vertical label positions (in case of a horizontal slider)

[hwiesmann]

The slider's label positions are wrongly calculated:

1. the distance between the slider's knob and the label is insufficient as the text overlaps with the knob when the slider has its best size
2. the label vertical positions in case of a horizontal slider (same holds for a vertical slider) are not adjusted when the slider's vertical size is below its best size

The effects can be seen by using the image sample program and opening the "Image filters test" window. I have attached two screen shots showing the two shortcomings.

Remark: the slider's background has been set by myself to red (I just did some investigations of the root cause and therefore needed a visual feedback) and is not part of the original source code.

This screenshot has been made when the window had been sufficiently enlarged.

This screenshot has been made when the height of the window had been reduced.

The reasons for the shortcomings are:

• wrong calculation of the distance between the slider's knob and the labels' texts
• not taking the size of the slider into account