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/r701_pair_i64_let_call/case.ww

@@ -0,0 +1,8 @@
+//ww:run-exit 8
+package main;
+type pair = struct { a: i64, b: i64 };
+fn mk() pair = { return pair { a = 3i64, b = 5i64 }; };
+fn main() i32 = {
+	let s: pair = mk();
+	return (s.a + s.b): i32;
+};