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/r773_spread_as_inline_payload/case.ww

@@ -0,0 +1,14 @@
+//ww:run-exit 7
+// Migrated from 773_isas_spread_variant row spread_as_inline_payload.
+package main;
+import io;
+type rsh = (size | io.eof | ...io.error);
+fn pick(b: i32) rsh = {
+    if (b == 1) { let u: io.underread = 7: i32: io.underread; return u; };
+    return 42: size;
+};
+export fn main() i32 = {
+    let r = pick(1);
+    let u = r as io.underread;
+    return u: i32;
+};