wcc: structlit repeat-fill dim off the stamped tinfo (rule 13)

cgstructlitfill's `...` total read only an N_INTLIT dim node, so a
def-dimensioned [N]T struct field under-filled: elements 1..N-1 kept
the zero-fill, silently, wwstage only (cstage and the tn twin read
the stamped array length). Read tichase(fi.tnode.type_).alen first;
the surface node stays as the fallback for unstamped shapes.

test/wcc/data/defdim_field_fill/case.ww

@@ -0,0 +1,16 @@
+//ww:run-exit 0
+// structlit `...` repeat-fill on a def-dimensioned [N]T field: the
+// fill total must come off the stamped array tinfo (rule 13). The
+// N_INTLIT-only surface read left elements 1..N-1 zero (ww-only).
+package main;
+def N: int = 4;
+type holder = struct { arr: [N]i64, tail: i64 };
+export fn main() i32 = {
+	let h: holder = holder{ arr = [7...], tail = 9 };
+	if (h.arr[0] != 7) { return 1; };
+	if (h.arr[1] != 7) { return 2; };
+	if (h.arr[2] != 7) { return 3; };
+	if (h.arr[3] != 7) { return 4; };
+	if (h.tail != 9) { return 5; };
+	return 0;
+};