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_branched_readers/case.ww

@@ -0,0 +1,26 @@
+//ww:run-exit 95
+// Migrated from 775_io_vtable_run row branched_readers.
+package main;
+import io;
+fn r1(s: io.stream, buf: []u8) (size | io.eof | io.error) = {
+    return 1: size;
+};
+fn r2(s: io.stream, buf: []u8) (size | io.eof | io.error) = {
+    return 2: size;
+};
+export fn main() i32 = {
+    let vt1: io.vtable;
+    let vt2: io.vtable;
+    vt1.reader = (&r1): *io.reader;
+    vt2.reader = (&r2): *io.reader;
+    let buf: [4]u8;
+    let bs: []u8 = buf[0:4];
+    let a = io.read(&vt1, bs);
+    let b = io.read(&vt2, bs);
+    let asz: size = 0;
+    let bsz: size = 0;
+    if (a is size) { asz = a as size; };
+    if (b is size) { bsz = b as size; };
+    if (asz == 1: size && bsz == 2: size) { return 95; };
+    return 99;
+};