`XmlReadContext` does not keep track of array index

[cowtowncoder]

Looks like location tracking for XmlReadContext does not update array index unlike other parsers. This makes path JsonReadContext.pathAsPointer() less useful than it could be.

[cowtowncoder]

Verifying the fix is actually trickier than initial fix since low-level FromXmlParser usage difficult.
So for now will just do manual verification via getParsingContext().pathAsPoint(), printing that out from tests.