Add XPath support for namespace-uri() condition and attribute elements

[evie-lau]

What's changed?

Add support for namespace-uri() conditions in XPathMatcher, along with tests
Add attribute match support in XPathMatcher (/@attributeName)
Update XPath splitter to handle URLs

What's your motivation?

Be able to use namespace filters in XPathMatcher

Anything in particular you'd like reviewers to focus on?

Anyone you would like to review specifically?

Have you considered any alternatives or workarounds?

Any additional context

Unsure about the addition of the new Interface Namespaced (or its naming). Just wanted to be able to run one of my methods on both Xml.Tag and Xml.Attribute objects.

Checklist

• I've added unit tests to cover both positive and negative cases
• I've read and applied the recipe conventions and best practices
• I've used the IntelliJ IDEA auto-formatter on affected files