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).
\w was the Perl word class (alphabetic, decimal, underscore). XSD 1.0 Datatypes
F.1 defines \w as [#x0000-#x10FFFF]-[\p{P}\p{Z}\p{C}], so symbols and marks are
word characters and the connector `_` (Pc) is not; \W is its complement and had
wrongly matched symbols. \w is now computed as "not punctuation, separator, or
other" via the category matcher.
XSTS: invalid instances accepted 231 to 210. The internal regex fixtures that
assumed `_` is a word character encoded Perl semantics and were corrected to the
XSD definition (symbols are word chars, `_` is not), confirmed against the XSTS
reV cases.
Refs #147, #129.
Grow the Tier-2 conformance corpus with 17 XSD regex cases through the
pattern-facet path: implicit whole-string anchoring, the character-class
escapes (backslash-d/w/s), Unicode category and negated-category escapes,
quantifier ranges (exact, bounded, open), alternation, grouping, negated
character classes, and class subtraction. All conform.
Part of #105 (Tier 2)
