UI: Add Manage Scene Collections dialog

[gxalpha]

Description

Adds a Scene Collection Manager dialog and moves the scene collection menu to the scenes dock.

Screenshots as of: September 8th, 2023

This solves three major UX problems with current scene collection management:

• The place where you'd manage scene collections was visually disconnected from the scene tree
• All actions were in a context menu, making them a bit cumbersome
• You could only act on the collection you're currently on. You couldn't rename, export, delete, or duplicate any other collection without switching to it first.

The new dialog solves these issues. Scene collection that aren't active can now be renamed, duplicated, exported, or deleted. However, the currently active scene collection can no longer be deleted as that would then require switching to some other collection, which can be a bit unpredictable to the user.

It also adds the ability to perform bulk actions on scene collections. This means that it's possible to duplicate, export, or delete multiple scene collections at once.
The collections shown in the menu is now capped at the 10 most recent ones to avoid unreasonably large context menus, other collections can still be switched to by double-clicking them in the dialog.

Driven by a design first approach, based on this mockup. Thanks to @GeorgesStavracas for creating the mockup and to @Warchamp7 for his assistance.

This PR utilizes new widgets by @derrod. It will stay draft until #8447 is merged. However, reviews are still very much desired.

Motivation and Context

See the problems mentioned above.

How Has This Been Tested?

macOS 13.2.1

Tested all new features. This includes:

• Opening the importer and importing
• Creating a new collection
• Renaming a collection (both current and not-current)
• Duplicating a collection (both current and not-current)
• Exporting a collection (both current and not-current) and making sure it's still sorted and pretty-printed (see UI: Sort and pretty-print exported collections #8407)
• Deleting a not-current collection
• Making sure the "Delete" field is greyed out and that the collection doesn't get deleted even if it isn't (by temporarily changing other code)
• Exporting multiple collections and making sure potential existing collections in the target folder aren't deleted
• Duplicating multiple collections
• Deleting multiple collections
• Switching scene collections via the menu in the scenes dock
• Switching scene collections by double-clicking a scene collection in the dialog
• Sorting works both by last used and alphabetically by name, and is remembered even after the dialog or OBS altogether is closed

Types of changes

• New feature (non-breaking change which adds functionality)

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.

[gxalpha]

Added Seeking Testers and re-triggered CI to get downloadable artifacts for easier testing.
Edit: This will need rebasing before artifacts actually get generated.

[gxalpha]

Rebased on the updated #8447.

New screenshot:

With the updated base branch, this should now actually have downloadable build artifacts once CI finishes.

[gxalpha]

Rebased on latest Idian branch. There are a few TODOs still left which I will fix later, plus a conflict to current master but that would require me to rebase the Idian branch as well.