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/r75_fromutf8_natural_match/case.ww

@@ -0,0 +1,6 @@
+//ww:run-exit 2
+package main;
+type invalid = !void;
+fn validate(s: str) (void | invalid) = { return; };
+fn fromutf8(s: str) (str | invalid) = { let v: (void | invalid) = validate(s); match (v) { case void => return s; case let e: invalid => return e; }; let e: invalid; return e; };
+fn main() i32 = { match (fromutf8("hi")) { case let s: str => return s.len: i32; case invalid => return -1; }; return 0; };