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/r83_assign_nil_nullable/case.ww

@@ -0,0 +1,5 @@
+//ww:run
+package main;
+type u = (*int | void);
+fn mk() u = { return nil; };
+export fn main() i32 = { return 0; };