Use Finalizable to ensure lexical liveness

[nielsenko]

We need to use the new Finalizable marker interface to ensure that native handles survive long enough. However, since Finalizables don't keep member finalizables alive, we also need to add a bunch of pseudo keepAlive extension methods, that are not exposed to the user, and only exists to teach the compiler about the lifetime dependencies of the various Finalizables.

Resolves: #581, resolves: #582

[nirinchev]

This looks reasonable, but still seems kind of hacky. I'm worried that a linker static analysis can discover those methods are unused and strip them from the compiled application. I'm not sure how much (if any) code stripping the dart linker does, especially when compiling to native, but it'd be interesting to confirm with the dart team this is the idiomatic approach for what we're trying to do.

[blagoev]

Added some suggestions. Also seems containing some debug left overs.

[nielsenko]

This looks reasonable, but still seems kind of hacky. I'm worried that a linker static analysis can discover those methods are unused and strip them from the compiled application. I'm not sure how much (if any) code stripping the dart linker does, especially when compiling to native, but it'd be interesting to confirm with the dart team this is the idiomatic approach for what we're trying to do.

See reply by dartlang developer here: dart-lang/sdk#49643 (comment)

I have actually chosen to make keepAlive an extension method, since (in my tests) it has the same effect, and it allows me to hide the otherwise public keepAlive from the user of our package. Perhaps you can confirm if this just as good, or not?

Yes this is fine, extension methods are basically top level methods with the receiver as first argument, and Finalizable arguments are kept alive.

[nielsenko]

BTW, in case it isn't obvious. The need to have these keepAlive extension methods should eventually disappear, once dart-lang/sdk#49643 is resolved.