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/r79_single_field_struct_assign/case.ww

@@ -0,0 +1,6 @@
+//ww:run-exit 42
+package main;
+type vtable = struct { x: i32 };
+type box = struct { src: *vtable };
+fn use(b: *box) i32 = { return b.src.x; };
+export fn main() i32 = { let vt: vtable; vt.x = 42; let b: box; b.src = &vt; return use(&b); };