UI: Fix remigrating scene collections from absolute to relative

[derrod]

Description

Fixes resetting scene collection base resolution to work again.

Motivation and Context

This was broken in #11055

How Has This Been Tested?

Locally.

Types of changes

• Bug fix (non-breaking change which fixes an issue)

Checklist:

• My code has been run through clang-format.
• I have read the contributing document.
• My code is not on the master branch.
• The code has been tested.
• All commit messages are properly formatted and commits squashed where appropriate.
• I have included updates to all appropriate documentation.

[Lain-B]

If we want to put this on a hotfix, we can merge this directly to a release branch if needed and not master, and then redo this for master after the UI changes are merged.

[Warchamp7]

If we want to put this on a hotfix, we can merge this directly to a release branch if needed and not master, and then redo this for master after the UI changes are merged.

We should try to get this out in a hotfix for sure

[PatTheMav]

I'm fine with fixing it on the release branch like this to get the issue fixed, but on master we need to find a different way. Adding a whole argument to ActivateSceneCollection that is not used in the vast majority of scenarios and thus requires to be set to false by default more or less telegraphs that it's not the correct way to do this.

So instead of carrying a remigrate flag around that is forwarded from nested function call to nested function call and only ever really processed by OBSBasic::LoadData, the requirement to remigrate should be part of the data that is loaded - you mark the data as "stale", which can then be read and detected by LoadData which then dutifully does the remigration.

Because ultimately no other method but OBSBasic::LoadData cares about this detail, so this detail should not leak into the internal API and function signatures.