Summary:
Implements a single confirmation dialog for multi-file deletion instead of prompting for each file individually. When users select multiple files or folders and choose to delete them via the context menu, they now see one confirmation dialog showing the total count of items to be deleted, rather than being prompted separately for each item.

• Added new localized messages (DeleteMultipleWarningMessage, RecycleMultipleWarningMessage, RecycleMultipleDirtyWarning) in const.ts to support batch deletion confirmations
• Refactored the deleteResource command in index.ts to collect all selected items and show a single confirmation based on the total count

Addresses #1290

Testing:
How did you test this change?

1. Sign in with a valid Viya connection
2. Open SAS Server or SAS Content in the explorer
3. Select multiple files and/or folders (use Cmd/Ctrl+Click or Shift+Click)
4. Right-click and select "Delete" from the context menu
5. Verify that only ONE confirmation dialog appears showing the count of items (e.g., "Are you sure you want to permanently delete 5 items?" or "Are you sure you want to move 3 items to the Recycle Bin?")
6. Test with a single file selection to ensure the original behavior is preserved (shows file name in confirmation)
7. Test with folders containing unsaved files to verify the appropriate warning message appears

TODOs:

• Add any supporting documentation and (optionally) update CHANGELOG.md