Moves the .vscode task filtering from the modal presentation layer
down into the inventory's worktree_scenarios(), so all consumers
get the correct behavior. Also filters previously spawned .vscode
tasks from the used-tasks list when .zed tasks are present.

The previous fix in zed-industries#32590 only filtered .vscode tasks in the
task picker modal, missing other code paths and the used-tasks list.

Fixes #51733

The previous fix in #32590 only filtered `.vscode` tasks at the modal
presentation layer, so they still appeared in other code paths and in
the used-tasks list. This moves the filtering into
`worktree_scenarios()` in the task inventory, so all consumers see the
correct behavior.

Changes:
- `InventoryFor::worktree_scenarios()` now skips `.vscode` entries when
`.zed` entries exist for the same worktree
- `used_and_current_resolved_tasks()` filters previously spawned
`.vscode` tasks from the used-tasks list
- Removes the now-redundant `.vscode` filter from the task picker modal

Release Notes:

- Fixed .vscode/tasks.json still being used when .zed/tasks.json is
present

Co-authored-by: moktamd <moktamd@users.noreply.github.com>