Auto merge of #6394 - nico-abram:unsafe_sizeof_count_copies, r=ebroto

Add lint size_of_in_element_count

Fixes #6381
changelog: Add lint to check for using size_of::<T> or size_of_val::<T> in the count parameter to ptr::copy or ptr::copy_nonoverlapping, which take a count of Ts (And not a count of bytes)

- \[X] Followed [lint naming conventions][lint_naming]
- \[X] Added passing UI tests (including committed `.stderr` file)
- \[ ] `cargo test` passes locally
- \[X] Executed `cargo dev update_lints`
- \[X] Added lint documentation
- \[X] Run `cargo dev fmt`

[lint_naming]: https://rust-lang.github.io/rfcs/0344-conventions-galore.html#lints

Running `cargo test` locally fails with this error:

```
running 1 test
test fmt ... FAILED

failures:

---- fmt stdout ----
status: exit code: 1
stdout:
stderr: error: unable to unlink old fallback exe
error: caused by: Access is denied. (os error 5)

thread 'fmt' panicked at 'Formatting check failed. Run `cargo dev fmt` to update formatting.', tests\fmt.rs:32:5
note: run with `RUST_BACKTRACE=1` environment variable to display a backtrace

failures:
    fmt

test result: FAILED. 0 passed; 1 failed; 0 ignored; 0 measured; 0 filtered out
```

But I did run `cargo dev fmt`

0 files changed, 0 insertions, 0 deletions