Fix issues with the budgets proposals import

[ahukkanen]

🎩 What? Why?

• Fix the scope selection with the proposals to projects import
• Do not import proposal if it is already imported to another budget within the same component
• Only import published and visible proposals

The issue was noticed when importing proposals to projects and using the scope selection. There has been an oversight with the migration done at #8669 as this case was not covered by the specs.

This issue can be seen when the following situation is applied:

• The participatory process has a scope defined
• Scopes are enabled for the budgets component and the default scope is the one defined for the process
• Importing proposals to projects will only import the proposals mapped to the default scope regardless of what was selected from the scopes selector

At the same time, I also noticed few other improvements that are implemented in this PR (see the list above).

📌 Related Issues

• Related to Migrate from Virtus to ActiveModel::Attributes (and get rid of Rectify::Form) #8669

Testing

• Create a top scope and some sub-scopes under it
• Create a participatory process and enable the top scope for the process
• Create proposals component and enable the top scope for the component
• Add some proposals to the component and pick scopes for them
• Evaluate some of the proposals as accepted
• Create a budgets component and enable the top scope for the component
• Create 2 budgets with different scopes than the top scope (i.e. one of the subscopes)
  • Make sure you have proposals mapped to those subscopes
• Import proposals to either one of these budgets by selecting the correct scope for them (i.e. the same scope that is defined for that budget)
• Import the proposals
• See that incorrect proposals were imported