common/math_util: Provide a template deduction guide for Common::Rectangle

Allows for things such as:

auto rect = Common::Rectangle{0, 0, 0, 0};

as opposed to being required to explicitly write out the underlying
type, such as:

auto rect = Common::Rectangle<int>{0, 0, 0, 0};

The only requirement for the deduction is that all constructor arguments
be the same type.