Adapt schema editors to operate from model states instead of fake rendered models

[Simon Charette]

Rendering models meant to be passed to the schema editor during the migrate phase is the main source of slowdown during the migrate phase of a project.

Adapting schema editors to be able to perform the same operations with model states would be way more efficient as model rendering could always be delayed until it's a necessity such during the application of RunPython operations.

Ref #22608.

Initial work by Markus Holtermann here ​https://github.com/django/django/compare/master...MarkusH:schemaeditor-modelstate

[Sanskar Jaiswal]

Hello everyone. This is the ​proposal that I submitted for GSoC, which unfortunately wasn't accepted. If it's fine, I would still like to work on this ticket. It would be amazing if I could get the above mentioned proposal reviewed and was given feedback, so that I know what to change and how to proceed.

Cheers

[Mariusz Felisiak <felisiak.mariusz@…>]

In d718d990:

Refs #29898 -- Moved django.db.migrations.operations.utils to django.db.migrations.utils.

[Mariusz Felisiak <felisiak.mariusz@…>]

In 503ee414:

Refs #29898 -- Moved state_forwards()'s logic from migration operations to ProjectState.

Thanks Simon Charette and Markus Holtermann for reviews.

[Carlton Gibson <carlton@…>]

In 54a30a7:

Refs #29898 -- Changed ProjectState.real_apps to set.

[Mariusz Felisiak <felisiak.mariusz@…>]

In 3e6a3e88:

Refs #29898 -- Refactored out ProjectState.resolve_model_relations()/resolve_model_field_relations() hooks.

[Mariusz Felisiak <felisiak.mariusz@…>]

In 196a99da:

Refs #29898 -- Made ProjectState encapsulate alterations in relations registry.

Thanks Simon Charette and Chris Jerdonek for reviews.

Co-authored-by: Mariusz Felisiak <felisiak.mariusz@…>

[GitHub <noreply@…>]

In fa1d7ba5:

Refs #29898 -- Changed fields in ProjectState's relation registry to dict.