More comprehensive type inference for pattern matching

[Nir Lisker]

Hi,

Give a simple generic wrapper,

class Container<T> {
    T item;
}

pattern matching can find out what T is for 'item', but not for its
container:

void switchItem(Container<?> container) {
    if (container.item instanceof Number num) {
        acceptNumber(num);
        acceptNumberContainer(container); // error
    }
}

The information is technically there to make the derivation. I can envision
some complexities with bound constraints, but seeing as I can't check
'instanceof Container<Number>`, can the compiler not be smarter?

- Nir
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