create_workspace_on_output: send workspace init event

create_workspace_on_output: send workspace init event

Fixes #3595
Like the issue mentions:
> instead of the newly created workspace (not referenced by variable
> here) the `"init"` event is fired with the current workspace (`ws`).

Plus, there was another issue where duplicate workspace init events
where being sent because of workspace_get().

304-ipc-workspace-init.t: Subtest "move workspace to output" fails with
current next.

Fixes #3631
No event was being sent here:
https://github.com/i3/i3/blob/2d6e09a66ad9b3e01588c515ae66476de8903754/src/randr.c#L487

533-randr15.t: I confirmed that SKIP still works if the xrandr command
fails.
Added test fails with current next.