Fix NoSuchMethodError: enablePendingPurchases() for Google Play Billing Library 7.x

[ptmkenny]

Problem

The plugin crashes on Android with the following error:

  java.lang.NoSuchMethodError: No virtual method
  enablePendingPurchases()Lcom/android/billingclient/api/BillingClient$Builder;
  in class Lcom/android/billingclient.api.BillingClient$Builder;
  at com.squareetlabs.capacitor.subscriptions.SubscriptionsPlugin.load(SubscriptionsPlugin.java:75)

Root Cause

The parameterless enablePendingPurchases() method was deprecated in Google Play Billing Library v7.0 and
removed in later versions. The plugin is using Billing Library v7.1.1 but still calling the old API.