Disable Add Discount product button if the order is loading

When Add Discount is tapped while the order is loading, the order totals are not loaded to calculate base price and discount correctly

Author: staskus

WooCommerce/Classes/ViewRelated/Orders/Order Creation/CollapsibleProductCard.swift

@@ -343,7 +343,7 @@ private extension CollapsibleProductRowCard {
                     onAddDiscount(viewModel.id)
                 }
                 .buttonStyle(PlusButtonStyle())
-                .disabled(shouldDisallowDiscounts)
+                .disabled(shouldDisallowDiscounts || isLoading)
             } else {
                 HStack {
                     Button(action: {
@@ -357,6 +357,7 @@ private extension CollapsibleProductRowCard {
                                 .frame(width: Layout.iconSize, height: Layout.iconSize)
                         }
                     })
+                    .disabled(isLoading)
                     Spacer()
                     if let discountLabel = viewModel.discountLabel {
                         Text(minusSign + discountLabel)