Default values for function arguments don't all match in c++ and python

[scpeters]

Many of our public APIs have some optional arguments with default values, but this can be inconsistent between our C++ and python APIs.

For example, the Plane class has only one optional argument in c++: _tolerance

gz-math/include/gz/math/Plane.hh

Lines 122 to 125 in 8292148

	public: std::optional<Vector3<T>> Intersection(
	const Vector3<T> &_point,
	const Vector3<T> &_gradient,
	const double &_tolerance = 1e-6) const

whereas all of its arguments are optional in python:

gz-math/src/python_pybind11/src/Plane.hh

Lines 79 to 85 in 8292148

	.def("intersection",
	&Class::Intersection,
	py::arg("_point") = gz::math::Vector3<T>::Zero,
	py::arg("_gradient") = gz::math::Vector3<T>::Zero,
	py::arg("_tolerance") = 1e-6,
	"Get the intersection of an infinite line with the plane, "
	"given the line's gradient and a point in parametrized space.")