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/r812_assign_24b_plain/case.ww

@@ -0,0 +1,4 @@
+//ww:run-exit 6
+package main;
+type st = struct { id: size, x: size, y: size };
+export fn main() i32 = { let a: st = st { id = 1: size, x = 2: size, y = 3: size }; let b: st = st { id = 0: size, x = 0: size, y = 0: size }; b = a; return (b.id + b.x + b.y): i32; };