`FromXmlParser` lacks extension point for passing custom `XmlTokenStream`

[xzxiaoshan]

Currently, the FromXmlParser class does not provide an extension point or factory mechanism to inject or use a custom implementation of XmlTokenStream. This limits the ability to perform advanced or customized XML parsing logic that may be required in certain use cases.

[cowtowncoder]

Merged for inclusion in 2.20.0.

Release will take a while, but I think release candidate(s) should be out during August.