Catch redundant member access casts in RedundantCast

[fourls]

Prerequisites

• [X] This improvement has not already been suggested.
• [X] This improvement should not be implemented as a separate rule.

Rule to improve

RedundantCast

Improvement description

The RedundantCast rule could be updated to catch cast expressions followed by a member access, in cases where the cast is not required to access the member.

For example:

type
  TMyClass = class(TObject)
  public
    procedure Foo;
  end;

// ...

procedure DoFoo(MyObj: TMyClass);
begin
  TMyClass(MyObj).Foo;
end;

Rationale

This improvement would catch a number of sneaky code smells that commonly occur when refactoring.

For example. consider a protected field on a class that is accessed from another unit by declaring a descendant class in the same unit, e.g.

// Unit1.pas

type
  TMyActualClass = class(TObject)
  protected
    procedure SecretProc;
  end;

// Unit2.pas

type
  TMyFriendClass = class(TMyActualClass);

procedure DoSecretProc(MyObj: TMyActualClass);
begin
  TMyFriendClass(MyObj).SecretProc;
end;

If a refactor changed TMyActualClass.SecretProc to public, the cast is no longer required to access SecretProc. This is easy to miss when refactoring and results in unnecessary complexity sticking around in the codebase.