Support Multiple Global Variable Sets

[brwarner]

Despite the ArticyFlowPlayer having a property called OverrideGVs, we did not actually properly support having multiple independent variable sets. You could duplicate the generated global variables asset, but it wouldn't be handled correctly and in some cases would crash the game.

We now support this workflow. To create a new global variables set, just duplicate the generated asset and move the new copy somewhere else in your project. Any flow player whose OverrideGV property is set to this asset will use this variable set instead of sharing the default set.

Similar to the default set, these other sets respect the Persist Global Variables Across Worlds setting.

[brwarner]

Basic functionality is working and tested. Just have to make sure it plays nice with source control and add a few helpers.

[brwarner]

Okay, I'm still getting an issue where existing global variable assets become corrupted if you add variable sets in Articy and import.

I may have to reimagine how this works unfortunately.

[brwarner]

Using dummy assets called Articy Alternative Global Variables to track that the user wants to use a different set of globals for various flow players. This solved all our hot reload disappearing asset issues. Plus it's a lot cleaner than dealing with duplicates of the global vars asset that need to be updated/reinitialized/etc.