System.Private.Xml AOT compatibility fixes

[jkoritzinsky]

Add some annotations for ILC as discovered in #75793

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Issue Details

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Add some annotations for ILC as discovered in #75793

Author:	jkoritzinsky
Assignees:	-
Labels:	area-System.Xml
Milestone:	-

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Issue Details

---

Add some annotations for ILC as discovered in #75793

Author:	jkoritzinsky
Assignees:	jkoritzinsky
Labels:	area-System.Xml, linkable-framework
Milestone:	-

[jkotas]

I assume that this warning is about values.ToArray(_itemType.ValueType). I think it works, but it fragile and hard to see that it is correct.

I would suggest factoring out the code that produces the Aot warning into a local method, apply the warning onto the local method only, and use the array type to create the array to guarantee that it is kept. Something like:

array = CreateArray(ListValueType);
values.CopyTo(array, 0);

...
[UnconditionalSuppressMessage("AotAnalysis", "Array type is passed as an argument to this method, so it is guaranteed to exist.")]
static Array CreateArray(Type arrayType, int length)
{
    Array array = Array.CreateInstance(arrayType.GetElementType()!, length);
    Debug.Assert(array.GetType() == arrayType);
    return array;
}

[jkotas]

Opened #76478 to make this better.

[radical]

/azp run runtime-wasm-libtests

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[eerhardt]

LGTM. It would be good to get sign off from a System.Xml owner.