WIP: usize alignment, pass size to roc_dealloc

[rtfeldman]

• Use usize instead of u32 for alignment in roc_alloc, roc_dealloc, and roc_realloc
• Pass size: usize to roc_dealloc (the number of bytes originally allocated by roc_alloc)

Currently this is rebased on top of https://github.com/rtfeldman/roc/pull/3524; once that lands, it should be merged into new-platform-functions, and then this should be rebased on top of new-platform-functions!

[github-actions[bot]]

Thank you for your contribution! Sometimes PRs end up staying open for a long time without activity, which can make the list of open PRs get long and time-consuming to review. To keep things manageable for reviewers, this bot automatically closes PRs that haven’t had activity in 60 days. This PR hasn’t had activity in 30 days, so it will be automatically closed if there is no more activity in the next 30 days. Keep in mind that PRs marked Closed are not deleted, so no matter what, the PR will still be right here in the repo. You can always access it and reopen it anytime you like!

[rtfeldman]

This is now so far off main I think it's gonna need to be redone.