Use the text selection background color for the scrollbar minimap slider
Previously, QPalette::link() was used which is the color for hyperlinks. Most themes set this to a shade of blue, so the slider will almost always be blue even when, for example, the main color of a theme is green.
The selection highlight color was chosen because it is also the color used for indicating the active tab and is, generally, often attuned to a theme's main color.
Below is a screenshot with a "bizarre" theme with the text highlight color set to purple, the (unvisited) hyperlink color to red, and the focus color to yellow.
