Auto merge of #107462 - WaffleLapkin:from_iterator_for_tuple, r=dtolnay

Implement `FromIterator` for `(impl Default + Extend, impl Default + Extend)`

Similarly to how rust-lang/rust#85835 implemented `Extend` for `(impl Extend, impl Extend)`:
```rust
impl<A, B, AE, BE> FromIterator<(AE, BE)> for (A, B)
where
    A: Default + Extend<AE>,
    B: Default + Extend<BE>,
{ ... }
```

Author: bors