`RegistryState`/`GlobalList` redundancy

[MaxVerevkin]

From what I understand, right now global handling is done in multiple steps:

1. waylad_client: GlobalList intercepts events and fills it's internal Mutex<Vec<Global>>. After the initial roundtrip it starts propagating new events.
2. client-toolkit: RegistryState clones the list of globals from GlobalList and keeps it in sync.

It seems that having two copies of Vec<Global> is redundant.