fix(core): Add checks for role presence before granting it

[aoyako]

Resolves #5246.

Verify that the role is present in the world before assigning it.

Example that should pass:

{
    "Register": {
        "Role": {
            "id": "good_role",
            "permissions": [
                {
                    "name": "CanSetParameters",
                    "payload": null
                }
            ],
            "grant_to": "ed0120E9F632D3034BAB6BB26D92AC8FD93EF878D9C5E69E01B61B4C47101884EE2F99@garden_of_live_flowers"
        }
    }
},
{
    "Grant": {
        "Role": {
            "object": "good_role",
            "destination": "ed0120CE7FA46C9DCE7EA4B125E2E36BDB63EA33073E7590AC92816AE1E861B7048B03@wonderland"
        }
    }
}

Example that should fail:

{
    "Grant": {
        "Role": {
            "object": "bad_role",
            "destination": "ed0120CE7FA46C9DCE7EA4B125E2E36BDB63EA33073E7590AC92816AE1E861B7048B03@wonderland"
        }
    }
}