Try symlinking proxies first, falling back to hardlinking if that fails

[ChrisDenton]

This reverse the previous order.

Closes#4022

[rami3l]

@ChrisDenton This PR looks good overall, I second @djc.

I have just one concern about what this would mean for existing users with existing hard links. Will this cause problems WRT upgrades?

[ChrisDenton]

Oh, looking at this I did find one issue, The raw::hardlink function sneakily includes a load bearing let _ = fs::remove_file(dest); call whereas there's no symlink equivalent. I should probably move that to a higher level rather than it being so implicit.

Otherwise there shouldn't be an issue as far as I can tell from the install_proxies function. We use the same-file crate to test if two handles/fds point to the same file. And we open the handle by following symlinks so it'll work in either case.

[rami3l]

Thanks for the explanation! I guess we can try this out as a part of the upcoming release.