debugger: Ensure both debug and regular global tasks are correctly merged (#27184)

Follow-up of https://github.com/zed-industries/zed/pull/13433
Closes https://github.com/zed-industries/zed/issues/27124
Closes https://github.com/zed-industries/zed/issues/27066

After this change, both old global task source, `tasks.json` and new,
`debug.json` started to call for the same task update method:


14920ab910/crates/project/src/task_inventory.rs (L414)

erasing previous declarations.

The PR puts this data under different paths instead and adjusts the code
around it.

Release Notes:

- Fixed custom tasks not shown

crates/project/src/project_settings.rs

@@ -24,7 +24,7 @@ use util::ResultExt;
 use worktree::{PathChange, UpdatedEntriesSet, Worktree, WorktreeId};
 
 use crate::{
-    task_store::TaskStore,
+    task_store::{TaskSettingsLocation, TaskStore},
     worktree_store::{WorktreeStore, WorktreeStoreEvent},
 };
 
@@ -642,7 +642,7 @@ impl SettingsObserver {
                 LocalSettingsKind::Tasks(task_kind) => task_store.update(cx, |task_store, cx| {
                     task_store
                         .update_user_tasks(
-                            Some(SettingsLocation {
+                            TaskSettingsLocation::Worktree(SettingsLocation {
                                 worktree_id,
                                 path: directory.as_ref(),
                             }),