OpenApi 3.1 namespace - support assigning `$schema` in every Schema Object

[char0n]

$schema must be accessible from every Schema Object without traversing it's parents. We'll use meta of Schema Element to store this information there. This needs to be implemented on refractor level and no resolution should be done at this phase.

[char0n]

This functionality was finally implemented as refractor plugin as all other options proved to be significantly more complex.