Add support for activating cutscenes via interact to EventTrigger

[aonkeeper4]

This PR adds a useInteract option to EventTrigger to allow activating the cutscene via an interact prompt, rather than via entering the trigger. To complement this, it also adds a deleteFlag option to allow preventing the trigger from loading via a flag. The reasoning behind this is that while doing the "don't load if this flag is set" logic in the cutscene works for activation via entering the trigger, for activation via interact, the interact prompt would still be visible even though the cutscene would not play.
Requires map editor support for 2 new attributes on eventTrigger: useInteract and deleteFlag.

[SilverDorian46]

I mean... on one hand, why not patch the InteractTrigger?
(preferably with a new CustomInteract attribute / event, since it uses different strings)

but on the other hand, yeah, the deleteFlag option may be useful.
or... you could maybe add a parameter (or two?) to the CustomEvent attribute, and that will check for whether a flag is set (or unset) before doing the cutscene

[aonkeeper4]

I feel patching InteractTrigger and using a second attribute would cause unnecessary duplication (I did want to patch it originally to use the same CustomEvent attribute, but that would require backwards-incompatible changes), and the only real difference in behaviour it has is the ability to trigger different cutscenes on sequential interacts. I don't mind taking this approach though if people agree it would be better.

[aonkeeper4]

I noticed InteractTriggers don't prevent themselves from activating multiple times in the same room, so I thought that an onlyOnce option (defaulting to true) would be a good idea to add too.
Also, I forgot to mention this in the PR body but the location of the interact prompt can be customized via the position of the trigger's node.

[Kalobi]

If we have any kind of "only once" option, we should definitely have one that's only once per session (so it remembers the interaction if you leave and reenter the room). At a glance, I don't think this option does that? See the "onlyOnce" vs "oncePerSession" flags in LuaCutscenes

[aonkeeper4]

Superseded by #1051.