Rollup merge of rust-lang#126347 - slanterns:try_simplify, r=scottmcm

Simplify `try_*`'s signature on `Iterator`

Inspired by rust-lang#126249 (comment).

r? `@scottmcm`

(Seems there's no need to explicitly use `<Self as Iterator>::Item`? I only find this occurrence across the whole file.)

library/core/src/iter/traits/iterator.rs

@@ -2080,8 +2080,7 @@ pub trait Iterator {
  fn try_collect<B>(&mut self) -> ChangeOutputType<Self::Item, B>
  where
  Self: Sized,
- <Self as Iterator>::Item: Try,
- <<Self as Iterator>::Item as Try>::Residual: Residual<B>,
+ Self::Item: Try<Residual: Residual<B>>,
  B: FromIterator<<Self::Item as Try>::Output>,
  {
  try_process(ByRefSized(self), |i| i.collect())
@@ -2689,12 +2688,13 @@ pub trait Iterator {
  #[inline]
  #[unstable(feature = "iterator_try_reduce", reason = "new API", issue = "87053")]
  #[rustc_do_not_const_check]
- fn try_reduce<F, R>(&mut self, f: F) -> ChangeOutputType<R, Option<R::Output>>
+ fn try_reduce<R>(
+ &mut self,
+ f: impl FnMut(Self::Item, Self::Item) -> R,
+ ) -> ChangeOutputType<R, Option<R::Output>>
  where
  Self: Sized,
- F: FnMut(Self::Item, Self::Item) -> R,
- R: Try<Output = Self::Item>,
- R::Residual: Residual<Option<Self::Item>>,
+ R: Try<Output = Self::Item, Residual: Residual<Option<Self::Item>>>,
  {
  let first = match self.next() {
  Some(i) => i,
@@ -2956,12 +2956,13 @@ pub trait Iterator {
  #[inline]
  #[unstable(feature = "try_find", reason = "new API", issue = "63178")]
  #[rustc_do_not_const_check]
- fn try_find<F, R>(&mut self, f: F) -> ChangeOutputType<R, Option<Self::Item>>
+ fn try_find<R>(
+ &mut self,
+ f: impl FnMut(&Self::Item) -> R,
+ ) -> ChangeOutputType<R, Option<Self::Item>>
  where
  Self: Sized,
- F: FnMut(&Self::Item) -> R,
- R: Try<Output = bool>,
- R::Residual: Residual<Option<Self::Item>>,
+ R: Try<Output = bool, Residual: Residual<Option<Self::Item>>>,
  {
  #[inline]
  fn check<I, V, R>(