Use JsonIOException for unchecked exceptions instead of RuntimeException in ConstructorConstructor

[panic08]

In the newDefaultConstructor method in ConstructorConstructor we throw RuntimeException when Failed to invoke constructor. However, as noted in the TODO, we should throw something specific like JsonIOException when an unchecked exception occurs. In this method we already throw JsonIOException on similar exceptions. I believe this change will give more readability, but more importantly, more semantic precision

[Marcono1234]

but more importantly, more semantic precision

But only due to using a Gson-specific exception instead of a generic RuntimeException. JsonIOException is still kind of 'wrong' for this because these issues are not IO related.

So I am a bit indecisive on this change. The underlying issue is that Gson has no proper exception hierarchy (#2359), and I am not sure if that can even be solved without breaking backward compatibility.

@eamonnmcmanus, what is your opinion?

---

Could you please adjust this test though to expect a JsonIOException now and remove the TODO comment there (I hope that is the only case):

gson/gson/src/test/java/com/google/gson/functional/ObjectTest.java

Line 733 in 44c9336

RuntimeException.class, () -> gson.fromJson("{}", ClassWithThrowingConstructor.class));

[panic08]

I agree that JsonIOException doesn't quite fit since it's typically used for IO related issues, but in my opinion it provides a bit more context than RuntimeException while we expect a more refined exception hierarchy in Gson (as discussed in #2359)