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/r771_direct_flat_variant/case.ww

@@ -0,0 +1,11 @@
+//ww:run-exit 71
+// Migrated from 771_widen_transitive row direct_flat_variant.
+package main;
+type underread = !i32;
+type nomem = !void;
+export fn main() i32 = {
+    let u: underread;
+    let r: (size | underread | nomem) = u;
+    if (r is underread) { return 71; };
+    return 99;
+};