Support `interface` generic constraint

[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 added a new interface constraint for generic types.
This ensures the type implements an interface.

See

• Interface Constraint

Rationale

Delphi 13 support.