[core] operator== hook

[jpeletier]

Note, requires #1454 to be merged first.

Building on the previous PR, this one adds a hook for operator==. It will detect this operator in a component definition and bind a hook to it that can be used to test components for equality.

If this operator is not defined but the compare operator is, Flecs will automatically derive this operator.

    class Vec2D {
    public:
        float x, y;
    
        Vec2D(float x = 0.0f, float y = 0.0f) : x(x), y(y) {}
    
        // Function to calculate the modulus (magnitude) of the vector
        float modulus() const {
            return std::sqrt(x * x + y * y);
        }
    
        // Overload operator< to compare vectors based on their modulus
        bool operator<(const Vec2D& other) const {
            return this->modulus() < other.modulus();
        }
    
        // Overload operator== to compare vectors with a precision tolerance of 0.001
        bool operator==(const Vec2D& other) const {
            return std::fabs(this->x - other.x) < 0.001 && std::fabs(this->y - other.y) < 0.001;
        }
    };

    flecs::world ecs;

    auto vtype =
        ecs.component<Vec2D>();  // will automatically register the above hooks.

    Vec2D a(1, 2);
    Vec2D b(2, 3);
    Vec2D c(1.00001, 1.9999999);

    const ecs_type_info_t *ti = ecs_get_type_info(ecs, vtype);

    assert(ti->hooks.equals(&a, &b, ti) == false); // ok!
    assert(ti->hooks.equals(&a, &c, ti) == true);  // ok!
    assert(ti->hooks.cmp(&b, &a, ti) > 0);         // ok!