pdl: derive `Copy` where possible

The advice from the standard library[1] is to make a type `Copy` if it
_can_ be `Copy`. Here we can simplify the code a bit by passing values
instead of references.

[1]: https://doc.rust-lang.org/std/marker/trait.Copy.html#when-should-my-type-be-copy

Test: atest pdl_tests pdl_inline_tests
Change-Id: Ib910dfb3ea297fae1b69a7a5571ba0ded365406e