Add manual_slice_size_calculation applicable suggestion

[timvisee]

Continuation of #10659 (comment).

This adds applicable suggestions to the manual_slice_size_calculation lint:

error: manual slice size calculation
  --> $DIR/manual_slice_size_calculation.rs:11:13
   |
LL |     let _ = s_i32.len() * size_of::<i32>(); // WARNING
   |             ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^ help: try: `std::mem::size_of_val(s_i32)`
   |
   = note: `-D clippy::manual-slice-size-calculation` implied by `-D warnings`

changelog: [manual_slice_size_calculation]: add machine applicable suggestion

[rustbot]

r? @Alexendoo

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[timvisee]

r? @Manishearth

[Manishearth]

@bors r+

thanks!

[bors]

📌 Commit a2580db has been approved by Manishearth

It is now in the queue for this repository.

[bors]

⌛ Testing commit a2580db with merge 203c909...

[bors]

☀️ Test successful - checks-action_dev_test, checks-action_remark_test, checks-action_test
Approved by: Manishearth
Pushing 203c909 to master...