Draft: rts/linker: Introduce finalizer support

Previously the linker made no attempt at invoking .fini finalizers when unloading an object. However, with the introduction of C++ objects into text it is more important that we respect the system ABI, lest we run the risk of resource leaks or worse.

Here we introduce finalizer support into the runtime linker, along with adding a test verifying that this behaves as expected with C++ objects.

Closes #20494 (closed).