Auto merge of #104818 - scottmcm:refactor-extend-func, r=the8472

Stop peeling the last iteration of the loop in `Vec::resize_with`

`resize_with` uses the `ExtendWith` code that peels the last iteration:
https://github.com/rust-lang/rust/blob/341d8b8a2c290b4535e965867e876b095461ff6e/library/alloc/src/vec/mod.rs#L2525-L2529

But that's kinda weird for `ExtendFunc` because it does the same thing on the last iteration anyway:
https://github.com/rust-lang/rust/blob/341d8b8a2c290b4535e965867e876b095461ff6e/library/alloc/src/vec/mod.rs#L2494-L2502

So this just has it use the normal `extend`-from-`TrustedLen` code instead.

r? `@ghost`

Author: bors