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/r800append_spread_str/case.ww

@@ -0,0 +1,12 @@
+//ww:run-exit 7
+package main;
+export fn main() i32 = {
+	let xs: []str = [];
+	let a: str = "abc";
+	let b: str = "fg";
+	append(xs, a);
+	let ys: []str = [];
+	append(ys, xs...);
+	append(ys, b);
+	return (ys[0].len + ys[1].len + ys.len): i32;
+};