Add the ability for tasks to target the center pane (#22004)

Closes #20060
Closes #20720
Closes #19873
Closes #9445

Release Notes:

- Fixed a bug where tasks would be spawned with their working directory
set to a file in some cases
- Added the ability to spawn tasks in the center pane, when spawning
from a keybinding:

```json5
[
  {
    // Assuming you have a task labeled "echo hello"
    "ctrl--": [
      "task::Spawn",
      { "task_name": "echo hello", "target": "center" }
    ]
  }
]
```

crates/editor/src/editor.rs

@@ -523,7 +523,7 @@ impl RunnableTasks {
     ) -> impl Iterator<Item = (TaskSourceKind, ResolvedTask)> + 'a {
         self.templates.iter().filter_map(|(kind, template)| {
             template
-                .resolve_task(&kind.to_id_base(), cx)
+                .resolve_task(&kind.to_id_base(), Default::default(), cx)
                 .map(|task| (kind.clone(), task))
         })
     }