New Rule: Class method should not be invoked from an object instance

[Skarvion]

Prerequisites

• [X] This rule has not already been suggested.
• [X] This should be a new rule, not an improvement to an existing rule.
• [X] This rule would be generally useful, not specific to my code or setup.

Suggested rule title

Class method should not be invoked from an object instance

Rule description

Calling a class method from an object instance would mislead reader that the method is an object method and may affect the object itself. Call class method using class name as prefix.

Rationale

// class declaration and implemeantion
type
  TFoo = class(TObject)
  public
    class procedure Bar;
  end;

implementation

class procedure TFoo.Bar;
begin
  // do something
end;

// calling
var
  FooObj: TFoo;
begin
  FooObj := TFoo.Create;
  FooObj.Bar; // non-compliant

  TFoo.Bar; // compliant
end.

[Cirras]

Agreed that a rule (or rules) to enforce "class constants/variables/methods should be referenced statically" would be useful.

[Cirras]

Class methods can be polymorphic, so we should probably exclude virtual class methods from the rule.