python: added Vector4 from Vector3 and Vector3 from Vector2 constructors.

Not sure why I missed those.

doc/python/pages/changelog.rst

@@ -35,6 +35,8 @@ Changelog
 `Changes since 2020.06`_
 ========================
 
+-   Exposed missing :ref:`Vector4` constructor from a :ref:`Vector3` and a
+    W component and :ref:`Vector3` from :ref:`Vector2` and a Z component
 -   Renamed :py:`Matrix3.from()` / :py:`Matrix4.from()` to :ref:`Matrix3.from_()`
     / :ref:`Matrix4.from_()` because :py:`from` is a Python keyword and it
     would be silly to have to write :py:`getattr(Matrix4, 'from')` just to use

src/python/magnum/math.vector.h

@@ -380,6 +380,7 @@ template<class T> void vector3(py::class_<Math::Vector3<T>>& c) {
     c
         /* Constructors */
         .def(py::init<T, T, T>(), "Constructor")
+        .def(py::init<Math::Vector2<T>, T>(), "Constructor")
         .def(py::init([](const std::tuple<T, T, T>& value) {
             return Math::Vector3<T>{std::get<0>(value), std::get<1>(value), std::get<2>(value)};
         }), "Construct from a tuple")
@@ -437,6 +438,7 @@ template<class T> void vector4(py::class_<Math::Vector4<T>>& c) {
     c
         /* Constructors */
         .def(py::init<T, T, T, T>(), "Constructor")
+        .def(py::init<Math::Vector3<T>, T>(), "Constructor")
         .def(py::init([](const std::tuple<T, T, T, T>& value) {
             return Math::Vector4<T>{std::get<0>(value), std::get<1>(value), std::get<2>(value), std::get<3>(value)};
         }), "Construct from a tuple")