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/r775_reader_set_happy/case.ww

@@ -0,0 +1,21 @@
+//ww:run-exit 70
+// Migrated from 775_io_vtable_run row reader_set_happy.
+package main;
+import io;
+fn myread(s: io.stream, buf: []u8) (size | io.eof | io.error) = {
+    return 7: size;
+};
+export fn main() i32 = {
+    let vt: io.vtable;
+    vt.reader = (&myread): *io.reader;
+    let v: io.stream = &vt;
+    let buf: [4]u8;
+    let bs: []u8 = buf[0:4];
+    let r = io.read(v, bs);
+    if (r is size) {
+        let n = r as size;
+        if (n == 7: size) { return 70; };
+        return 71;
+    };
+    return 99;
+};