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_f64/case.ww

@@ -0,0 +1,5 @@
+//ww:run-exit 35
+package main;
+type u = (f64 | str);
+fn mk() u = { return 3.5; };
+export fn main() i32 = { let v = mk(); match (v) { case let f: f64 => return 35; case str => return 1; }; return 9; };