Make `cursor.blinkCanceled` public so that it can be handled

**Is your feature request related to a problem? Please describe.**
I'm writing a `tea.Model` that wraps around a `bubbles.textinput` and a few other bubbles.
In my `Update` method, I have a switch statement on the `msg.(type)`, in which I handle certain messages I send myself but forward for instance `tea.KeyMsg` to the inner `textinput`. I want to include a default case to that switch statement that panics, so that I ensure I don't accidentally forgot to handle a message type while developing.

Now the issue occurs when the inner `textinput` is Focus'd, because then `cursor.blinkCanceled` messages sometimes pass through the `Update` chain, which triggers the panic I have.
This wouldn't be a problem if I could simply have `case cursor.blinkCanceled:`, but since `blinkCanceled` is local to the cursor package the compiler won't let me catch it.

**Describe the solution you'd like**
`type cursor.blinkCanceled...` -> `type cursor.BlinkCanceled...` so that the type is exposed to the outside.

**Describe alternatives you've considered**
For now I've disabled blinking altogether on the inner `textinput`, but that feels like a shame!

**Additional context**

**Update:**
Actually, setting `input.Cursor.Blink = false` doesn't appear to prevent the `blinkCanceled` messages from being fired. Would there be another way to prevent these messages from being fired?