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_nested/case.ww

@@ -0,0 +1,5 @@
+//ww:run-exit 6
+package main;
+type inner = struct { x: size, y: size };
+type outer = struct { tag: size, i: inner };
+export fn main() i32 = { let a: outer = outer { tag = 1: size, i = inner { x = 2: size, y = 3: size } }; let b: outer = outer { tag = 0: size, i = inner { x = 0: size, y = 0: size } }; b = a; return (b.tag + b.i.x + b.i.y): i32; };