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/r681_slice_field_value_write/case.ww

@@ -0,0 +1,9 @@
+//ww:run-exit 42
+package main;
+type bs = struct { rbuf: []u8, mark: i32 };
+fn main() i32 = {
+	let raw: [8]u8; raw[0] = 0u8; let rbuf: []u8 = raw[0:5]; let b: bs;
+	b.mark = 7; b.rbuf = rbuf;
+	if (b.rbuf.len != 5) { return 1; }; if (b.rbuf.cap != 8) { return 2; };
+	if (b.mark != 7) { return 3; }; return 42;
+};