Fix lint `manual_slice_size_calculation` when a slice is ref more than once
When a slice is ref more than once, current suggestion given by `manual_slice_size_calculation` is wrong. For example:
```rs
let s: &[i32] = &[1, 2][..];
let ss: &&[i32] = &s; // <-----
let _ = size_of::<i32>() * ss.len();
```
clippy now suggests:
```patch
- let _ = size_of::<i32>() * ss.len();
+ let _ = size_of_val(ss);
```
However, this can result in calculating the size of `&[i32]`, instead of `[i32]` (this wrong suggestion also leads to `size_of_ref` warning: https://rust-lang.github.io/rust-clippy/master/index.html#/size_of_ref )
Now I am sending this PR to fix this bug, so that clippy will suggest (some deref added):
```patch
- let _ = size_of::<i32>() * ss.len();
+ let _ = size_of_val(*ss);
```
As I am not familiar with current clippy code-base, please correct me if I am not doing well or I can do it better :)
changelog: [`manual_slice_size_calculation`]: fix a bug when a slice is ref more than once.
6a281e9a73