* Introduce `WP_Customize_Manager::get_nonces()` to consolidate logic for retrieving nonces.
* Export nonces centrally in `wp.customize.settings.nonce` with each request and update nav menus preview to utilize.
* Send updated nonces to preview upon `nonce-refresh`.
* Request full preview refresh if Nav Menu selective refresh request fails (e.g. due to bad nonce).
* Update nav menus and widgets in Customizer to utilize `customize_refresh_nonces` for exporting nonces and keeping them up to date.
See #27355.
Fixes#35617.
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