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/r989_callarg_scalar_for_slice/case.ww

@@ -0,0 +1,4 @@
+//ww:error "not assignable"
+package main;
+fn takesslice(xs: []int) void = { return; };
+export fn main() int = { let n: int = 5; takesslice(n); return 0; };