add CloneFromCopy and Cell::get_cloned

[Qelxiros]

Tracking issue: #145329

[rustbot]

r? @tgross35

rustbot has assigned @tgross35.
They will have a look at your PR within the next two weeks and either review your PR or reassign to another reviewer.

Use r? to explicitly pick a reviewer

[rust-log-analyzer]

The job pr-check-2 failed! Check out the build log: (web) (plain enhanced) (plain)

Click to see the possible cause of the failure (guessed by this bot)

---- library/core/src/cell.rs - cell::Cell<T>::get_cloned (line 754) stdout ----
error[E0433]: failed to resolve: use of undeclared type `Rc`
 --> library/core/src/cell.rs:760:10
  |
9 | let rc = Rc::new(1usize);
  |          ^^ use of undeclared type `Rc`
  |
help: consider importing this struct
  |
6 + use std::rc::Rc;