test/wcc/data: grow the declarative compiler corpus to 1,224 fixtures

The r-prefixed waves absorb the runtime, reject, and byte-compare rows
of the migrated native carriers; each fixture is one directory with one
case.ww and a //ww:error, //ww:compile, //ww:run, or //ww:run-exit
directive covering both frontends.

test/wcc/data/r989_m1union_invalid/case.ww

@@ -0,0 +1,17 @@
+//ww:run-exit 4
+package main;
+import encoding.utf8;
+fn classify(d: *utf8.decoder) int = {
+	match (utf8.next(d)) {
+	case let r: rune => return 1;
+	case let dn: utf8.done => return 2;
+	case let m: utf8.more => return 3;
+	case let e: utf8.invalid => return 4;
+	};
+	return 0;
+};
+export fn main() int = {
+	let s: []u8 = [255u8];
+	let d = utf8.decode(s);
+	return classify(&d);
+};