• Export SpecVisitor, ClosureExpression, LiteralMapExpression
LiteralRecordExpression, LiteralSetExpression types.
• Support Expression.newInstanceNamed with empty name
• Consistently add blank lines between => in class-like definitions.
• Fixed bug: Fields declared with static and external now produce code with
  correct order
• Require built_collection: ^5.1.1
• Require built_value: ^8.10.1
• Require collection: ^1.19.0
• Require matcher: ^0.12.16+1
• Require meta: ^1.16.0
• Require sdk: ^3.7.0