cgen: peel *fn field types for local struct-field callees

fnptrcalleetfn's N_DOT arm accepted only a bare N_TFN field tnode, so
a call through a field declared `cb: *fn(...)` missed, fell through to
the name registry, and emitted CALL cb(SB) — an undefined symbol
(loud at link; cstage calls the stamped ptr-to-fn indirectly). Same
TPTR peel the N_IDENT arm already had. Fixture fnptrfield_call covers
the by-value and via-pointer shapes; corpus pin 1478/2956.

test/wcc/data/fnptrfield_call/case.ww

@@ -0,0 +1,22 @@
+//ww:run-exit 36
+package main;
+
+// A call through a struct field declared `*fn(...)`, by value and via
+// pointer. The wwstage fnptrcalleetfn N_DOT arm lacked the TPTR peel
+// its N_IDENT arm had, so the callee fell through to the name registry
+// and emitted CALL cb(SB) — an undefined symbol.
+
+type cbs = struct {
+	cb: *fn(x: i32) i32,
+	k:  i32,
+};
+
+fn twice(x: i32) i32 = { return x * 2; };
+
+fn main() i32 = {
+	let o: cbs;
+	o.cb = &twice;
+	o.k = 4;
+	let p: *cbs = &o;
+	return o.cb(10) + p.cb(6) + o.k;
+};