Sketch: add command to context-menu to change value of constraint

The edit datum dialog is opened by double-clicking on a dimensional constraint in a sketch. However, the double-clicking event doesn't work realiably on
some systems. As a workaround this PR adds the command to the context-menu.

For more details see the forum thread: https://forum.freecad.org/viewtopic.php?t=71137

src/Mod/Sketcher/Gui/CommandConstraints.cpp

@@ -9778,6 +9778,59 @@ bool CmdSketcherConstrainSnellsLaw::isActive()
     return isCreateConstraintActive(getActiveGuiDocument());
 }
 
+// ======================================================================================
+DEF_STD_CMD_A(CmdSketcherChangeDimensionConstraint)
+
+CmdSketcherChangeDimensionConstraint::CmdSketcherChangeDimensionConstraint()
+    : Command("Sketcher_ChangeDimensionConstraint")
+{
+    sAppModule = "Sketcher";
+    sGroup = "Sketcher";
+    sMenuText = QT_TR_NOOP("Change value");
+    sToolTipText = QT_TR_NOOP("Change the value of a dimensional constraint");
+    sWhatsThis = "Sketcher_ChangeDimensionConstraint";
+    sStatusTip = sToolTipText;
+    eType = ForEdit;
+}
+
+void CmdSketcherChangeDimensionConstraint::activated(int iMsg)
+{
+    Q_UNUSED(iMsg);
+
+    auto getDimConstraint = []() {
+        std::vector<Gui::SelectionObject> selection{getSelection().getSelectionEx()};
+        if (selection.size() != 1 || selection[0].getSubNames().size() != 1) {
+            throw Base::RuntimeError();
+        }
+
+        if (auto sketch = dynamic_cast<Sketcher::SketchObject*>(selection[0].getObject())) {
+            std::string subName = selection[0].getSubNames().at(0);
+            if (subName.size() > 10 && subName.substr(0, 10) == "Constraint") {
+                int ConstrId = Sketcher::PropertyConstraintList::getIndexFromConstraintName(subName);
+                return std::make_tuple(sketch, ConstrId);
+            }
+        }
+
+        throw Base::RuntimeError();
+    };
+
+    try {
+        auto value = getDimConstraint();
+        EditDatumDialog editDatumDialog(std::get<0>(value), std::get<1>(value));
+        editDatumDialog.exec(false);
+    }
+    catch (const Base::RuntimeError&) {
+        Gui::TranslatedUserWarning(getActiveGuiDocument()->getDocument(),
+                                   QObject::tr("Wrong selection"),
+                                   QObject::tr("Select one dimensional constraint from the sketch."));
+    }
+}
+
+bool CmdSketcherChangeDimensionConstraint::isActive()
+{
+    return isCommandActive(getActiveGuiDocument());
+}
+
 // ======================================================================================
 /*** Creation Mode / Toggle to or from Reference ***/
 DEF_STD_CMD_AU(CmdSketcherToggleDrivingConstraint)
@@ -10053,6 +10106,7 @@ void CreateSketcherCommandsConstraints()
     rcCmdMgr.addCommand(new CmdSketcherConstrainPointOnObject());
     rcCmdMgr.addCommand(new CmdSketcherConstrainSymmetric());
     rcCmdMgr.addCommand(new CmdSketcherConstrainSnellsLaw());
+    rcCmdMgr.addCommand(new CmdSketcherChangeDimensionConstraint());
     rcCmdMgr.addCommand(new CmdSketcherToggleDrivingConstraint());
     rcCmdMgr.addCommand(new CmdSketcherToggleActiveConstraint());
     rcCmdMgr.addCommand(new CmdSketcherCompDimensionTools());

src/Mod/Sketcher/Gui/ViewProviderSketch.cpp

@@ -4142,6 +4142,9 @@ void ViewProviderSketch::generateContextMenu()
 
         // context menu if only constraints are selected
         else if (selectedConstraints >= 1) {
+            if (selectedConstraints == 1) {
+                menu << "Sketcher_ChangeDimensionConstraint";
+            }
             menu << "Sketcher_ToggleDrivingConstraint"
                  << "Sketcher_ToggleActiveConstraint"
                  << "Sketcher_SelectElementsAssociatedWithConstraints"