Create TODO declarations for unresolved parent scopes

[Morriar]

Consider this:

class Foo::Bar
  def bar; end
end

Right now, if we can't resolve Foo, we won't create a definition for Bar and will end up creating bar() under object: Object#bar().

With this PR, we try to resolve everything then, for the remaining definition we couldn't resolve, we enter in a mode where we create TODO declaration for the missing ones and try to resolve what it unblocks.

So for our example the logic would look like this:

1. Normal process mode
  1.1. Try to resolve `Bar` -> Unresolved parent scope `Foo`
  1.2. Re-enque `Bar`
  1.3. Continue until the queue is empty or we can't make progress anymore

2. We still have definitions in the queue but couldn't make progress => start Todo process mode
  2.1. Try to resolve `Bar`
  2.2. Create `Foo` as a Todo declaration under `Object`
  2.3. Create `Foo::Bar` under `Foo`
  2.4. Continue until the queue is empty or we can't make progress anymore

3. Process the remaining definitions (methods, etc.)
  3.1. Create `bar()` under `Bar`

[vinistock]

Why does this need to change?

[vinistock]

Instead of looping through the queue twice, can we not incorporate Todo in the regular processing?

If we eagerly create unresolved definitions as Todo, while still enqueuing a retry, we could do everything in a single loop.

Maybe in combination with #505