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_str_field/case.ww

@@ -0,0 +1,4 @@
+//ww:run
+package main;
+type named = struct { id: size, name: str };
+export fn main() i32 = { let a: named = named { id = 7: size, name = "hello" }; let b: named = named { id = 0: size, name = "" }; b = a; if (b.id != 7) { return 1; }; if (b.name.len != 5) { return 2; }; return 0; };