Follow-up of https://github.com/zed-industries/zed/pull/22004
* Reuse center terminals for tasks, when requested
* Extend task templates with `RevealTarget`, moving it from
`TaskSpawnTarget` into the core library
* Use `reveal_target` instead of `target` to avoid misinterpretations in
the task template context
* Do not expose `SpawnInTerminal` to user interface, avoid it
implementing `Serialize` and `Deserialize`
* Remove `NewCenterTask` action, extending `task::Spawn` interface
instead
* Do not require any extra unrelated parameters during task resolution,
instead, use task overrides on the resolved tasks on the modal side
* Add keybindings for opening the task modal in the
`RevealTarget::Center` mode
Release Notes:
- N/A
bc113e4b51