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/r650_slice_field_pseudo/case.ww

@@ -0,0 +1,9 @@
+//ww:run-exit 5
+package main;
+type bag = struct { buf: []u8, x: i32 };
+fn main() i32 = {
+	let arr: [8]u8; let i: i32 = 0;
+	for (i < 8) { arr[i] = i: u8; i = i + 1; };
+	let b: bag; b.buf.ptr = &arr[0]; b.buf.len = 5; b.buf.cap = 8; b.x = 0;
+	return b.buf.len;
+};