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_branched_callee_widen/case.ww

@@ -0,0 +1,19 @@
+//ww:run-exit 45
+// Migrated from 774_tagged_widen_named_variant row branched_callee_widen.
+package main;
+type unsupported = !void;
+type wrapper = !(unsupported);
+type eof = void;
+fn pick(b: bool) (size | eof | wrapper) = {
+    if (b) {
+        let u: unsupported;
+        let e: wrapper = u;
+        return e;
+    };
+    return 50: size;
+};
+export fn main() i32 = {
+    let r1 = pick(true);
+    let r2 = pick(false);
+    return 45;
+};