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/r946_structret_i64f64_ret/case.ww

@@ -0,0 +1,9 @@
+//ww:run
+package main;
+type pif = struct { a: i64, b: f64 };
+fn mk() pif = { return pif { a = 3, b = 5.0 }; };
+export fn main() i32 = {
+	let s: pif = mk();
+	if (s.a + (s.b: i64) != 8) { return 1; };
+	return 0;
+};