Implement `Clone + Copy` for `ContextRef`

[Gavrilikhin Daniil]

Is your feature request related to a problem? Please describe.
create_debug_location accepts the following argument: context: impl AsContextRef<'ctx>.

I store context: ContextRef<'ctx> from module, when creating debug info builder, but it's not clonnable

Describe the solution you'd like
Copyable ContextRef

Describe possible drawbacks to your solution
Safety issues possibly?

[Dan Kolsoi]

Will have to think about any possible safety concerns some more... That said, I think it'd be ok to make it clone or maybe even copy.

[Dan Kolsoi]

The 'ctx lifetime effectively makes it a reference to the original Context, so I think Copy would be safe