Remove leaky synchronisation objects.

[LorrensP-2158466]

fixes #3967

The pr is structured in 4 commits, the first two replace the use of Id with Ref objects. The third commit refactors the declare_id! macro into a macro that creates these Ref objects for us. The last commit removes the usage of SynchronisationObjects.

[LorrensP-2158466]

@rustbot ready

[RalfJung]

Thanks a lot! Looks good overall, except I don't think this macro is worth it -- sorry.

[RalfJung]

@rustbot author

[rustbot]

Reminder, once the PR becomes ready for a review, use @rustbot ready.

[LorrensP-2158466]

@rustbot ready

[RalfJung]

Ah, you force-pushed... please avoid that if at all possible (except when I ask you to do it), it makes it a lot harder to track what happened since the last review. (This is a pretty fatal flaw in Github, but unless they eventually get better at dealing with force-pushes we all have to work around it manually.)

[RalfJung]

In this case you probably had to force-push to remove that macro commit, but you did not have to incorporate any of the recent changes in master. git rebase --keep-base helps in that case.

[RalfJung]

The existing concerns are resolved, but you added a bunch of new changes I didn't ask for so there's new concerns.^^
@rustbot author

[LorrensP-2158466]

Ah, you force-pushed... please avoid that if at all possible (except when I ask you to do it), it makes it a lot harder to track what happened since the last review.

Ah shit, sorry. I'll remember that!

[LorrensP-2158466]

Tests should be fine, the latest changes were just some refactorings.

@rustbot ready

[RalfJung]

This looks great, thanks! Please squash the commits using ./miri squash. Then write @rustbot ready after you force-pushed the squashed PR.

@rustbot author

[LorrensP-2158466]

@rustbot ready