UI: dim icons in inactive tabs, similar to text

This makes the properties editor navigation bar less saturated. Internally
the icon theme coloring was refactored a bit to move more towards the button
drawing code.

source/blender/editors/interface/interface_panel.c

@@ -771,7 +771,8 @@ void ui_draw_aligned_panel(uiStyle *style,
                     (block->aspect / UI_DPI_FAC),
                     1.0f,
                     0.0f,
-                    (const char *)col_title);
+                    (const char *)col_title,
+                    false);
     GPU_blend(false);
   }