Variables improvements

- Refactor properties value getter into a delegate.
- Fix list parsing from string.
- Improve empty variable syntax identifier regex.
- Refactor ConditionEvaluator move BuildContext out of it.
- Add support for data and variable overrides.
- Add data source for list view and update transformer to use that data source.

Author: BirjuVachhani

lib/src/api/extensions.dart

@@ -29,7 +29,7 @@ extension StringExtensions on String {
     } else if (R == List) {
       try {
         return value
-            .substring(1, value.length - 2)
+            .substring(1, value.length - 1)
             .split(',')
             .map((e) => e.trim().parsedValue())
             .toList() as R?;

lib/src/api/regexes.dart

@@ -126,7 +126,7 @@ final RegExp variablePathComposingRegex = RegExp(variablePathComposingPattern);
 const String variableSyntaxIdentifierPattern = r'\${(?<value>.+)}';
 
 /// A regex that can match empty ${} syntax with partial match for curly braces.
-const String emptyVariableSyntaxIdentifierPattern = r'\${?}?';
+const String emptyVariableSyntaxIdentifierPattern = r'^\${?}?$';
 
 /// Regex for [emptyVariableSyntaxIdentifierPattern].
 final RegExp emptyVariableSyntaxIdentifierRegex =