Hide fallback choices after loading

[tvararu]

Fixes #959.

This preserves the isInvisibleDefault flag by adding it to serialisation and deserialisation.

Add a regression test to ensure it works correctly. I haven't tested the C# version manually, but I did as part of my PR to inkjs.

That PR contains more details about the exact analysis of the bug; I haven't duplicated it here as it's basically the same.

All tests pass:

Starting test execution, please wait...
A total of 1 test files matched the specified pattern.

Passed!  - Failed:     0, Passed:   358, Skipped:     0, Total:   358, Duration: 535 ms