apply-templates and for-each keep attribute and namespace nodes in
their selections; the context carries the non-tree current node with
its owner element backing the tree-only machinery, XPath evaluation
and current() start from it, match patterns select attribute nodes
through attribute identities in the match cache, the built-in rules
copy an attribute's or namespace's value as text, xsl:copy copies the
focused attribute or declaration itself, and an attribute result
arriving after element content is ignored (the XSLT recovery).
Sorting, for-each, and choose move to XSLTSorting.swift for the file
caps. Xalan baseline 352 -> 292 (axes 35 -> 16, copy 29 -> 16).
Mihaela Mihaljevic
b41678064e