tasks: Add editor: Spawn Nearest Task action (#19901)

This spawns the runnable task that that's closest to the cursor.

One thing missing right now is that it doesn't find tasks that are
attached to non-outline symbols, such as subtests in Go.

Release Notes:

- Added a new reveal option for tasks: `"no_focus"`. If used, the tasks
terminal panel will be opened and shown, but not focused.
- Added a new `editor: spawn nearest task` action that spawns the task
with a run indicator icon nearest to the cursor. It can be configured to
also use a `reveal` strategy. Example:
```json
{
  "context": "EmptyPane || SharedScreen || vim_mode == normal",
  "bindings": {
    ", r t": ["editor::SpawnNearestTask", { "reveal": "no_focus" }],
  }
}
```


Demo:



https://github.com/user-attachments/assets/0d1818f0-7ae4-4200-8c3e-0ed47550c298

---------

Co-authored-by: Bennet <bennet@zed.dev>

docs/src/tasks.md

@@ -18,6 +18,7 @@ Zed supports ways to spawn (and rerun) commands using its integrated terminal to
     "allow_concurrent_runs": false,
     // What to do with the terminal pane and tab, after the command was started:
     // * `always` — always show the terminal pane, add and focus the corresponding task's tab in it (default)
+    // * `no_focus` — always show the terminal pane, add/reuse the task's tab there, but don't focus it
     // * `never` — avoid changing current terminal pane focus, but still add/reuse the task's tab there
     "reveal": "always",
     // What to do with the terminal pane and tab, after the command had finished: