Correctly display a color when using search marks in the minimap
This fixes 2 issues regarding the minimap search marks. First, it
was using the global theme instead of the current one. This meant
changing the theme using the Settings->Editor color theme
didn't
change the minimap markers color. The second was that the search
marks are displayed, but don't have a "real" color. Adding a new
color wasn't possible because it requires to add en entry in an
enum at a specific location, which breaks the ABI. Using
KSyntaxHighlighting::Theme::EditorColorRole::SearchHighlight
is "close enough" and better than a fully black rectangle on a
dark background.
That conditional isn't exactly elegant, but due to how the code is designed (using arithmetic on enum values), all "sane" fixes break the ABI.