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/r774_accept_pure_leaf_subset/case.ww

@@ -0,0 +1,11 @@
+//ww:run-exit 43
+// Migrated from 774_tagged_widen_named_variant row accept_pure_leaf_subset.
+package main;
+type ax = !void;
+type bx = !void;
+type cx = !void;
+fn small() (ax | bx) = { let u: ax; return u; };
+export fn main() i32 = {
+    let r: (ax | bx | cx) = small();
+    return 43;
+};