The xsl:key match was turned into a path by prepending //, but for a union
match like "Level1 | Level2" the // applied only to the first branch
(//Level1 | Level2), so the second branch matched relative to the root and
found nothing, dropping those nodes from the key. Distribute // over each
top-level union branch (// inside a predicate or function call is left alone).
Closes Apache Xalan conformance cases idkey45, idkey46, idkey47, idkey48.
Group @testable imports at the bottom, per public/rules-swift's swiftformat. A
behavior-preserving import-ordering reformat across 252 files (mostly tests).
--trailingclosures was deliberately not adopted (cosmetic, and swiftformat flags
it as caution-worthy).
key(name, node-set), including key('k', .), now unions the indexed nodes
for every value node's string value and de-duplicates, instead of using
only the first node's string value. A string value still works directly.
Part of #82.
