Support `is not` operator

[cirras]

Prerequisites

• This improvement has not already been suggested.
• This improvement would be generally useful, not specific to my code or setup.

Engine area

Delphi language support

Improvement description

Delphi 13 has introduced a new is not operator.

Example

if not (Obj is TFoo) then ... // classic syntax
if Obj is not TFoo then ... // new syntax

See

• The is not and not in Operators

Rationale

Delphi 13 support.