NodeStateTable.GetModifiedItemAndState does not guard against a throwing .Equals method

[chsienki]

When the comparer used here:

roslyn/src/Compilers/Core/Portable/SourceGeneration/Nodes/NodeStateTable.cs

Lines 557 to 564 in 9db0f39

	private static (T chosen, EntryState state, bool chosePrevious) GetModifiedItemAndState(T previous, T replacement, IEqualityComparer<T> comparer)
	{
	// when comparing an item to check if its modified we explicitly cache the *previous* item in the case where its
	// considered to be equal. This ensures that subsequent comparisons are stable across future generation passes.
	return comparer.Equals(previous, replacement)
	? (previous, EntryState.Cached, chosePrevious: true)
	: (replacement, EntryState.Modified, chosePrevious: false);
	}

is not a user supplied comparer, and the call to T.Equals() throws, we don't catch the exception and convert into a UserFunctionException. This can cause a generator to bring the hosting process down. We should always wrap default comparers in a user wrapped user comparer to ensure we still do the translation.

See here for an example: microsoft/CsWinRT#1897