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/r76_infer_struct_u32_i64_decf/case.ww

@@ -0,0 +1,6 @@
+//ww:run-exit 20
+package main;
+type decf = struct { mantissa: u32, exponent: i64 };
+fn make(flag: i32) decf = { if (flag == 0) { return decf { mantissa = 7u32, exponent = 13i64 }; }; return decf { mantissa = 99u32, exponent = -1i64 }; };
+fn use_(d: decf, which: i32) i32 = { if (which == 0) { return ((d.mantissa: i64) + d.exponent): i32; }; return ((d.mantissa: i64) - d.exponent): i32; };
+fn main() i32 = { let d = make(0); return use_(d, 0); };