Add vaulting component module boilerplate

[Dinamiko]

This PR introduces a feature flag (PCP_VAULT_COMPONENT_ENABLED) that gates the entire Vault Component functionality.

When disabled (default), checkout behaves exactly as today. When enabled, the plugin loads the Vault Component module and evaluates customer eligibility (logged in, has saved PayPal token, vault capability active, US region for alpha). This also includes passing the necessary vault data (token ID, eligibility) to the frontend JavaScript for both classic and block checkout.

[github-actions]

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What's included:

• ✅ WordPress (latest)
• ✅ WooCommerce (latest)
• ✅ PayPal Payments plugin v4.0.2-pr4267-24193793726-g83f21e7 (built from this PR)

Login credentials:

• Username: admin
• Password: password

Plugin Details:

• Version: 4.0.2-pr4267-24193793726-g83f21e7
• Commit: 26c1ccb
• Artifact: woocommerce-paypal-payments-4.0.2-pr4267-24193793726-g83f21e7

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