feat(flame_jenny): Public access to variables to allow load/save (#2689)

Allows direct access to the variables in the VariableStorage class in jenny (via YarnProject.variables.variables).

This enables a user to implement a save game feature to save the variables and later restore them.

doc/other_modules/jenny/runtime/index.md

@@ -15,5 +15,6 @@ FunctionStorage    <function_storage.md>
 MarkupAttribute    <markup_attribute.md>
 Node               <node.md>
 UserDefinedCommand <user_defined_command.md>
+VariableStorage    <variable_storage.md>
 YarnProject        <yarn_project.md>
 ```

doc/other_modules/jenny/runtime/variable_storage.md

@@ -0,0 +1,7 @@
+# VariableStorage
+
+```{dartdoc}
+:package: jenny
+:symbol: VariableStorage
+:file: src/variable_storage.dart
+```

doc/other_modules/jenny/runtime/yarn_project.md

@@ -75,6 +75,12 @@ final yarn = YarnProject()
 **trueValues**, **falseValues** `Set<String>`
 : The strings that can be recognized as `true`/`false` values respectively.
 
+**variables** `VariableStorage`
+: The [container][VariableStorage] for all variables declared and manipulated in your yarn scripts.
+  This is also used for maintaining the visit counts for nodes that the user has visited. To
+  implement a 'save game' feature it is possible to save the variables from
+  `VariableStorage.variables` and later restore them again.
+
 
 ## Methods
 
@@ -92,3 +98,4 @@ final yarn = YarnProject()
 [CommandStorage]: command_storage.md
 [FunctionStorage]: function_storage.md
 [Node]: node.md
+[VariableStorage]: variable_storage.md

packages/flame_jenny/jenny/lib/src/variable_storage.dart

@@ -1,10 +1,8 @@
 import 'package:jenny/src/errors.dart';
 import 'package:jenny/src/structure/expressions/expression.dart';
 import 'package:jenny/src/structure/expressions/variables.dart';
-import 'package:meta/meta.dart';
 
 class VariableStorage {
-  @protected
   final Map<String, dynamic> variables = <String, dynamic>{};
 
   int get length => variables.length;