[FR] Add a templated constructor to `juce::var` that uses `juce::VariantConverter` to construct the var

It’s really nice being able to implicitly construct a juce::var from types that it supports, e.g.

void setValue (juce::var value);

setValue ("Hello, World!");
setValue (123);

However, when you want to set a custom type for which you’ve specified a juce::VariantConverter, suddenly it’s not so nice:

struct MyCoolClass{};

struct VariantConverter<MyCoolClass> {};

setValue (juce::VariantConverter<MyCoolClass>::toVar (myCoolObject));

It’d be really nice if there were a templated constructor for juce::var that used juce::VariantConverter internally, and perhaps an operator T() as well?

template<typename T>
var::var (const T& value)
    *this = VariantConverter<T>::toVar (value);

template<typename T>
T var::operator T() const
    return VariantConverter<T>::fromVar (*this);