#5811 false postive: (error) Null pointer dereference
Fix regression from first attempt fixing #5811 (9dce9bddcbbddb252653367f0e39a4c77108f5eb)
Partially rewritten AST compilation:
 - More straightforward approach for handling right-to-left associativity
 - More straightforward approach to handling unary operators
 - Improved handling of brackets

This fixes #5784, #5795, #5797, #5799, #5810 and a bunch of other problems
Refactorization: Use AST in CheckOther::checkRedundantCopy(), CheckOther::clarifyStatement() and CheckPostfixOperator::postfixOperator().