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_mix_let_call/case.ww

@@ -0,0 +1,8 @@
+//ww:run-exit 10
+package main;
+type mix = struct { a: i32, b: i32, c: i64, d: i64 };
+fn mk() mix = { return mix { a = 1, b = 2, c = 3i64, d = 4i64 }; };
+fn main() i32 = {
+	let s: mix = mk();
+	return (s.a + s.b) + (s.c + s.d): i32;
+};