Find usages doesn't work well inside the file that included by `include!` macro

```rust
// ./src/lib.rs
include!("foo.rs");

fn howdy() {
    let _ = FIND_ME;
         // ^^^^^^^ triggering find usages here works fine
    println!("{FIND_ME}");
            // ^^^^^^^ fine here, too
}

// ./src/foo.rs
const FIND_ME: i32 = 0;
   // ^^^^^^^ not finding any usages here
```
