Google Play: Improve upgrade check reliability

[d4rken]

Previously we used orderId to check for valid purchases but apparently this is not a reliable way to check state.

While documentation says:

The order ID will be null if the purchase is in the Purchase.PurchaseState.PENDING state and populated if the purchase has transitioned to the Purchase.PurchaseState.PURCHASED state.

in reality I could reproduce cases where the orderId field was null despite getPurchaseState() == PURCHASED. What up Google?

My best guess so far is that the cached data that queryPurchasesAsync sometimes returns, does not always contain all fields. Clearing Google Play cache can reset it and fix that, but it's unclear why and when the "half-cached" state returns.

A normal, fully cached purchase entry looks like this:

{
    "orderId": "GPA.<id>",
    "packageName": "eu.darken.sdmse",
    "productId": "eu.darken.sdmse.iap.upgrade.pro",
    "purchaseTime": 1697351226769,
    "purchaseState": 0,
    "purchaseToken": "<token>",
    "quantity": 1,
    "acknowledged": true
}

A half-cached entry looks like this:

{
    "packageName": "eu.darken.sdmse",
    "productId": "eu.darken.sdmse.iap.upgrade.pro",
    "purchaseTime": 1680023656958,
    "purchaseState": 0,
    "purchaseToken": "<token>"
}

While the json payload contains purchaseState == UNSPECIFIED, the actual Purchase.getPurchaseState() function still returns PURCHASED in the half-cached state. Due to fallback handling:

    public int getPurchaseState() {
        switch (this.zzc.optInt("purchaseState", 1)) {
            case 4:
                return 2;
            default:
                return 1;
        }
    }

So this PR changes the check to getPurchaseState.