Move task centering code closer to user input (#22082)

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

crates/editor/src/editor.rs

@@ -522,7 +522,7 @@ impl RunnableTasks {
     ) -> impl Iterator<Item = (TaskSourceKind, ResolvedTask)> + 'a {
         self.templates.iter().filter_map(|(kind, template)| {
             template
-                .resolve_task(&kind.to_id_base(), Default::default(), cx)
+                .resolve_task(&kind.to_id_base(), cx)
                 .map(|task| (kind.clone(), task))
         })
     }