UI: Restore frontend API events being dispatched during initialization

[PatTheMav]

Description

Restore dispatch of frontend events that have not been dispatched due to prior refactor.

Motivation and Context

The frontend API events "OBS_FRONTEND_EVENT_SCENE_CHANGED" and "OBS_FRONTEND_EVENT_PREVIEW_SCENE_CHANGED" are not dispatched if disableSaving has a value > 0. Prior code decremented disableSaving to 0 globally (regardless of whether saving was necessary, which is only the case if a new collection is created as a fallback for a missing scene collection).

Thus the updated code exhibits different event dispatch behavior then old code which some plugins might have relied on. To avoid introducing new behavior, explicitly create the environment to allow the dispatch to take place and remove/refactor the events in a later version.

How Has This Been Tested?

Checked frontend dispatch taking place with existing scene collection, scene collection name provided via command-line argument as well as with missing scene collection.

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]

I thought this would have been called elsewhere but I guess we need to explicitly call them 🤔

[gxalpha]

I haven't been able to check whether it's actually the case, but noticed in code OBS_FRONTEND_EVENT_SCENE_COLLECTION_LIST_CHANGED and OBS_FRONTEND_EVENT_SCENE_COLLECTION_CHANGED may also be effected. Noting this down so that it maybe doesn't get forgotten.

[Lain-B]

Yeah doesn't prevent this one from being merged but it would probably be good to double-check any others if we suspect they could be affected.

[PatTheMav]

I thought this would have been called elsewhere but I guess we need to explicitly call them 🤔

They are called before, but disableSaving is always non-zero (and has to be in the case of existing collections, otherwise they might be overwritten by half-initialised collection state at program start), so no actual dispatch happens.

IMO it is more correct that none of these events are dispatched before OBS is initialised, but that change should happen after communicating this change, so I'm fine with adding workarounds for them until then.

[gxalpha]

Can confirm that this solves the situation where I found the problem.

[RytoEX]

Nit: initialisation -> initialization

Looks good otherwise.