Add version builder

lib/licenses.dart

@@ -1,5 +1,4 @@
 import "dart:io";
-
 import "package:build/build.dart";
 import "package:dart_pubspec_licenses/dart_pubspec_licenses.dart";
 import "package:yaml/yaml.dart";

lib/version.dart

@@ -0,0 +1,29 @@
+import "dart:io";
+import "package:build/build.dart";
+import "package:yaml/yaml.dart";
+
+class VersionBuilder implements Builder {
+  @override
+  Future build(BuildStep step) async {
+    final pubspecFile = loadYaml(
+      await File('pubspec.yaml').readAsString(),
+    );
+
+    String fileContent = '''
+//// AUTO-GENERATED by build_runner ////
+/// DO NOT EDIT BY HAND
+part of "version.dart";
+
+const pubspecVersionString = '${pubspecFile["version"]}';
+''';
+
+    await step.writeAsString(step.allowedOutputs.first, fileContent);
+  }
+
+  @override
+  final buildExtensions = const {
+    "pubspec.yaml": [ "lib/shared/version.moxxy.dart" ]
+  };
+}
+
+Builder versionBuilder(BuilderOptions _) => VersionBuilder();