ipn/ipnlocal: rename web fields/structs to webClient

For consistency and clarity around what the LocalBackend.web field
is used for.

Updates tailscale/corp#14335

Signed-off-by: Sonia Appasamy <sonia@tailscale.com>

ipn/ipnlocal/web_client_stub.go

@@ -0,0 +1,27 @@
+// Copyright (c) Tailscale Inc & AUTHORS
+// SPDX-License-Identifier: BSD-3-Clause
+
+//go:build ios || android
+
+package ipnlocal
+
+import (
+	"errors"
+	"net"
+
+	"tailscale.com/client/tailscale"
+)
+
+type webClient struct{}
+
+func (b *LocalBackend) SetWebLocalClient(lc *tailscale.LocalClient) {}
+
+func (b *LocalBackend) WebClientInit() error {
+	return errors.New("not implemented")
+}
+
+func (b *LocalBackend) WebClientShutdown() {}
+
+func (b *LocalBackend) handleWebClientConn(c net.Conn) error {
+	return errors.New("not implemented")
+}