[BUG] Generated union copy constructor can be invalid

[KendallHarter]

Describe the bug
Copying a union can result in invalid pointers errors.

To Reproduce
Sample code:

test: @union type = {
   name: std::string;
}

main: () = {
   a1: test = ();
   a1.set_name("hi");
   a2 := a1;
}

Commands:

./cppfront test.cpp2
g++11.3 -I ./include/ -std=c++20 test.cpp
./a.out

Expected result:
Program runs without error.

Actual result/error:

munmap_chunk(): invalid pointer
Aborted

Additional context
This seems to be caused by the implicit member-wise copying having no opt-out option, as it'll copy the storage before potentially deleting it with the set_name function.

[JohelEGP]

Yes.
It copies the storage and discriminator.
So it believes it has a live object when the set_* first calls destroy().

[JohelEGP]

Smells like #475.

[JohelEGP]

The general operator= should default-initialize the storage and set the discriminator to -1.
Better yet, overload operator=: (inout this, that); to not assign {} to the storage.

[JohelEGP]

Resolved by commit cdf71bd.