Feature request: Be able to update all existing toasts without knowing their ids

**Do you want to request a *feature* or report a *bug*?**
Feature

---
**What is the current behavior?**
When I want to update a toast, I have to know its id
```typescript
toats.update(toastId, { /* options */ })
```
---
**What is the expected behavior?**
I want to update all current toasts that are showing on the screen, without knowing all their ids and iterating through.
```typescript
toast.update(null, { /* options */ }) // or another signature like `toast.update(options)`
```
It will work just like `toast.dismiss()` which closes all existing toasts without passing all their ids in.

Start by reading the existing toast.update and toast.dismiss entry points to understand their current argument handling and how dismissing all toasts is exposed. Compare the proposed update signatures, then verify that the chosen behavior updates every currently displayed toast without requiring individual ids and preserves existing id-based updates.

Written by the indexing model from the issue text.