[TechDraw]Detail highlight drag (fix #21828) (#22036)

* [TD]add preferences for detail highlight snapping

* [TD]fix highlight drag issues

* Update src/Mod/TechDraw/Gui/TaskDetail.cpp

minor format change from benj5378.

Co-authored-by: Benjamin Bræstrup Sayoc <benj5378@outlook.com>

---------

Co-authored-by: Benjamin Bræstrup Sayoc <benj5378@outlook.com>

src/Mod/TechDraw/App/Preferences.cpp

@@ -693,3 +693,15 @@ bool Preferences::showUnits()
 }
 
 
+bool Preferences::snapDetailHighlights()
+{
+    return Preferences::getPreferenceGroup("General")->GetBool("SnapHighlights", true);
+}
+
+
+//! distance within which we should snap a highlight to a vertex
+double Preferences::detailSnapRadius()
+{
+    return getPreferenceGroup("General")->GetFloat("DetailSnapRadius", 0.6);
+}
+