refactor: rename variable name to more readable form

packages/deriv_ui/lib/components/numpad/core/exchange_notifier.dart

@@ -118,9 +118,9 @@ class ExchangeController extends ChangeNotifier {
   ///  what user send by default in primaryCurrency when coming to numpad.)
   double finalAmount() {
     if (_exchangeRate.baseCurrency == primaryCurrency.currencyType) {
-      return primaryCurrency.finalAmount;
+      return primaryCurrency.formattedAmount;
     } else {
-      return secondaryCurrency.finalAmount;
+      return secondaryCurrency.formattedAmount;
     }
   }
 }

packages/deriv_ui/lib/components/numpad/models/currency_detail.dart

@@ -37,26 +37,26 @@ class CurrencyDetail {
   bool get isFiat => fiatCurrencies.contains(currencyType);
 
   /// This will check if the currency is stable coin currency(USDC,tUSDT,eUSDT) or not.
-  bool get isStableCurrency =>
+  bool get isStableCryptoCurrency =>
       stableCurrencies.contains(currencyType.toUpperCase());
 
   /// This will give the final amount to do processing based on what type of currency it is like fiat or crypto currency.
-  double get finalAmount => double.parse(formatter.format(amount));
+  double get formattedAmount => double.parse(formatter.format(amount));
 
   /// Amount that is used to display for user.
   String get displayAmount {
     if (amount == 0.0) {
       return '';
     }
 
-    return isFiat || isStableCurrency
+    return isFiat || isStableCryptoCurrency
         ? amount.toStringAsFixed(2)
         : amount.toStringAsFixed(8);
   }
 
   /// This will give a specific currency formatter based on what type of currency it is like fiat or crypto currency.
   NumberFormat get formatter {
-    if (isFiat || isStableCurrency) {
+    if (isFiat || isStableCryptoCurrency) {
       return NumberFormat('#0.##', 'en_US');
     } else {
       return NumberFormat('#0.########', 'en_US');