Add a lint for items used before definition,inside expression block

I would like to have a lint like the items_after_statements lint,but which only triggers if an item defined inside an expression block is used before it's defined.

For example,it would trigger with this code:

fn hello() {
    println!("First statement");
    let hello: Bar = (0..10).collect();
    type Bar = Vec<u32>;
}

But it would not trigger with this code:

fn hello() {
    println!("First statement");
    type Bar = Vec<u32>;
    let hello: Bar = (0..10).collect();
}

Start by locating Clippy's existing items_after_statements lint and its tests, then inspect how expression blocks and item definitions are represented. The change is done when a lint reports an item used before its definition only within an expression block, while allowing the reversed order shown in the issue.