Do not mark constants as seen before generating RBI for them

[Morriar]

Motivation

Fix foreign constants mixin for already seen ancestors

Consider the following example when running tapioca gem gemB:

# gemA code
class Bar; end

# gemB code
module Foo; end
class Baz < Bar; end
Bar.prepend Foo

While visiting the constants of GemB we would:

• visit constant Baz
• visit the superclass constant Bar
• mark Bar as seen
• skip Bar since it belongs to GemA
• visit the foreign constant Bar for the prepend
• skip Bar because previously marked as seen

Implementation

Only mark a constant as seen if we generate something for it.

Tests

See included test.

[paracycle]

Good catch! Thank you

[egiurleo]

👏🏻