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/r56_cast_i16_high_bits/case.ww

@@ -0,0 +1,9 @@
+//ww:run-exit 42
+package main;
+fn main() i32 = {
+	let x: i64 = 0xFFFF8000i64;
+	let y: i16 = x: i16;
+	let z: i64 = y: i64;
+	if (z == -32768i64) { return 42; };
+	return 0;
+};