Automatically promote constants to namespaces

[vinistock]

This PR does two main things:

• Removes all of the todos with the skips we had in resolution for constants
• Handles some meta-programming scenarios without crashing

Although we can't provide first class features when there's meta-programming, we absolutely cannot crash. Consider these examples (or the ones added as tests):

Foo = dynamic_module

class Bar
  include Foo
end

Baz = dynamic_class

class Qux < Baz
end

module Zip; end

Boop = dynamic_class do
  include Zip
end

This PR takes two strategies to prevent crashing completely in these scenarios:

• The most straightforward one is just skipping things that aren't namespaces during ancestor linearization. If we find an include for something that's not a namespace, we need to skip it
• The second part is auto-promoting constants to namespaces if they get re-opened. This allows us to handle this scenario correctly (which we actually have in Core):

# At this point, we have no idea this is a class. We create a Constant declaration for it
Const = dynamic_class

# Then it gets re-opened as a class with proper includes
class Const
  include Foo
end

By auto-promoting, we correctly handle ancestors and constant resolution for Const. Of course, there's a concession being made to the user here: we trust that they didn't make a mistake by making an incompatible re-opening (i.e.: it was a module, then gets reopened as a class).

[vinistock]

• Add integrity check for owner relationships #592
• Automatically promote constants to namespaces #505 👈 (View in Graphite)
• main

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[Morriar]

Could you rebase on either #474 or #502 (depending on the one you want to accept) so we can see the impact on diagnostics?

[st0012]

I think it may be possible to further extend this approach in follow up PRs to also promote cases like:

Foo = some_method do
  include Bar # doing mixing stuff
  def baz; end # defining methods
end

In this PR, we already promote Foo when it's reopened for those operations, so IMO it makes sense to promote the above cases too. And it'd be a foundation for a basic DSL support.

@vinistock and I talked about this idea yesterday but it's not confirmed whether it'd be feasible/ideal or not.

Other than this, I think the PR is good to merge so we can index Core again.

[vinistock]

I added a test to document the current behaviour. Meta-programmed namespaces don't get auto promoted at the moment. That would involve inspecting to see if there are members inside, which is a bit much for this PR, but might be an avenue we want to explore for DSL handling.