TY: several type inference fixes

[vlad20012]

1. Fix lambda parameter type inference. This fixes a case where a lambda is assigned to a variable and types on lambda parameters should be inferred later:

fn main() {
    let a = |b| {
        b;
    };//^ i32
    foo(a);
}

fn foo<T: FnOnce(i32)>(_: T) {}

2. Fix ? operator with Try trait. The (unstable) Try trait was moved to core::ops::try_trait::Try and its associated types was renamed. Now ? works for Poll<Result>, for example.

use std::task::Poll;
fn foo(p: Poll<Result<i32, ()>>) -> Result<(), ()> {
    let a = p?;
    a;
  //^ Poll<i32>
    Ok(())
}

3. Fix for loop over type parameter implementing Iterator:

fn foo<I: Iterator<Item = i32>>(a: I) {
    for b in a {
        b;
    } //^ i32
}

4. Derive recently added unstable Destruct trait for all types. It is used as a trait bound in stdlib

[mchernyavsky]

bors r+

[bors]

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