Add AnyMemberOperator + subclasses

- AnyMemberOperator (RedHat’s MemberOperator)
- MemberOperator (RedHat’s MemberOp)
- SafeMemberOperator (RedHat’s SafeMemberOp)
- SpreadMemberOperator (RedHat’s SpreadOp)

For #58; however, the issue isn’t closed yet, because we still have to
integrate AnyMemberOperator into QualifiedExpression.
Add tests for AnyMemberOperator + subclasses
nameWithTypeArguments: make convenience function more convenient

by defaulting the typeArguments parameter to null
QualifiedExpression: Add AnyMemberExpression child

Closes #58.
Add tests for #58 (QualifiedExpression member op)

Also adds a construct() function to QualifiedExpression and changes all
tests to use that. So much more readable!