Removal of deprecated constants & query syntax

[SanderMertens]

The deprecated INSTANCEOF, CHILDOF, TRAIT and Singleton constants are removed from the codebase. Additionally, the deprecated trait query syntax has also been removed. The last commit before these changes is: 65353d6

Make sure to update code to the replacements:

C API:

// Old
ecs_add_id(world, e, ECS_INSTANCEOF | base);
// New
ecs_add_pair(world, e, EcsIsA, base);
// Or
ecs_add_id(world, e, ecs_pair(EcsIsA, base));

// Old
ecs_add_id(world, e, ECS_CHILDOF | parent);
// New
ecs_add_pair(world, e, EcsChildOf, parent);
// Or
ecs_add_id(world, e, ecs_pair(EcsChildOf, parent));

// Old
ecs_set(world, EcsSingleton, Position, {10, 20});
// New
ecs_singleton_set(world, Position, {10, 20});

C++ API:

// Old
e.add(flecs::Instanceof | base);
// New
e.add(flecs::IsA, base);
// Or
e.is_a(base);

// Old
e.add(flecs::Childof | parent);
// New
e.add(flecs::ChildOf, parent);
// Or
e.child_of(parent);

Query syntax:

// Old
TRAIT | Rel > Obj
Rel FOR Obj
// New
(Rel, Obj)

// Old
TRAIT | Rel
PAIR | Rel
// New
(Rel, *)

// Old
$:Position
// New
$Position