script: Fix two issues in the XPath parser to pass all xml_xpath_tests.xml tests (#37279)

1. Better handling of namespaces for element and attribute names in XML
mode (read: non-HTML mode)
2. While parsing, pass along context on whether we are in an absolute
(`/`) or descendant (`//`) part of the query, and use it to correctly
enumerate descendants according to where we are in the evaluation of the
AST.

Testing: All 1024 tests in `xml_xpath_tests.xml` (actually
`xml_xpath_runner.html`) pass, as well as some random tests in
`text-html-attributes.html`.
Fixes: #37278

---------

Signed-off-by: Ville Lindholm <ville@lindholm.dev>

components/script/xpath/context.rs

@@ -5,10 +5,14 @@
 use std::iter::Enumerate;
 use std::vec::IntoIter;
 
+use script_bindings::str::DOMString;
+
 use super::Node;
+use crate::dom::bindings::codegen::Bindings::NodeBinding::NodeMethods;
 use crate::dom::bindings::root::DomRoot;
 
 /// The context during evaluation of an XPath expression.
+#[derive(Debug)]
 pub(crate) struct EvaluationCtx {
     /// Where we started at
     pub(crate) starting_node: DomRoot<Node>,
@@ -20,7 +24,7 @@ pub(crate) struct EvaluationCtx {
     pub(crate) predicate_nodes: Option<Vec<DomRoot<Node>>>,
 }
 
-#[derive(Clone, Copy)]
+#[derive(Clone, Copy, Debug)]
 pub(crate) struct PredicateCtx {
     pub(crate) index: usize,
     pub(crate) size: usize,
@@ -68,6 +72,12 @@ impl EvaluationCtx {
             size,
         }
     }
+
+    /// Resolve a namespace prefix using the context node's document
+    pub(crate) fn resolve_namespace(&self, prefix: Option<&str>) -> Option<DOMString> {
+        self.context_node
+            .LookupNamespaceURI(prefix.map(DOMString::from))
+    }
 }
 
 /// When evaluating predicates, we need to keep track of the current node being evaluated and