A user reported to me that they are unable to create a PSBT with a legacy watchonly wallet when they use the GUI. They get an error "The amount exceeds your balance".

I think the issue is that the GUI will retrieve the wallet's balance via `AvailableCoins` before calling `CreateTransaction`. This call to `AvailableCoins` is resulting in fewer coins being returned with recent changes to how `AvailableCoins` works, particularly with additional filtering of spendable coins and preset coins.

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Note that this does not effect descriptor wallets. A workaround for this issue is to switch to using descriptor wallets. An existing legacy wallet can be turned into a descriptor wallet using the `migratewallet` RPC. However many watchonly legacy wallets are likely the result of importing descriptors via `importmulti`. For such wallets, I recommend creating a new descriptor wallet and re-importing the descriptors.
{
    // 
    m_coin_control->fAllowWatchOnly = model->wallet().privateKeysDisabled() && !model->wallet().hasExternalSigner();
    // 
    CAmount amount = model->getAvailableBalance(m_coin_control.get());
    for (int i = 0; i < ui->entries->count(); ++i) {
        SendCoinsEntry* e = qobject_cast<SendCoinsEntry*>(ui->entries->itemAt(i)->widget());
        if (e && !e->isHidden() && e != entry) {
            amount -= e->getValue().amount;
        }
    }
    if (amount > 0) {
      entry->checkSubtractFeeFromAmount();
      entry->setAmount(amount);
    } else {
      entry->setAmount(0);
    }
}
void SendCoinsDialog::updateFeeSectionControls()
{
    ui->confTargetSelector      ->setEnabled(ui->radioSmartFee->isChecked());
    ui->labelSmartFee           ->setEnabled(ui->radioSmartFee->isChecked());
    ui->labelSmartFee2          ->setEnabled(ui->radioSmartFee->isChecked());
    ui->labelSmartFee3          ->setEnabled(ui->radioSmartFee->isChecked());
    ui->labelFeeEstimation      ->setEnabled(ui->radioSmartFee->isChecked());
    ui->labelCustomFeeWarning   ->setEnabled(ui->radioCustomFee->isChecked());
    ui->labelCustomPerKilobyte  ->setEnabled(ui->radioCustomFee->isChecked());
    ui->customFee               ->setEnabled(ui->radioCustomFee->isChecked());
}
void SendCoinsDialog::updateFeeMinimizedLabel()