addVariable method
Add variable to specific scope
Implementation
void addVariable(String scope, String name, dynamic value) {
_context['scopes'] ??= <String, dynamic>{};
final scopes = _context['scopes'] as Map<String, dynamic>;
scopes[scope] ??= <String, dynamic>{};
final scopeData = scopes[scope] as Map<String, dynamic>;
scopeData[name] = value;
}