Add boolean check to isEqual function, and adds two other functions

[MikeCaputo]

One fix and two new functions

1. As of Gamemaker release 2.3.7.603 (https://gms.yoyogames.com/ReleaseNotes.html), I found that a struct with a value of true was being evaluated as True within the IDE, whereas before it was evaluated as a 1. This was causing Gamemaker to fail, because the isEqual function did not have a boolean comparator.
2. Separately, adds two new functions:
   i. indexOf, which returns the index of an item within a collection.
   ii. flatArrayIncludes, which can only check flat arrays but is more performant than the includes function.

[MikeCaputo]

Oops, I'm not sure why it's bringing in all three of these commits, @DatZach . Let me know if you want me to create a new PR. Also, this merge request bundles a couple of different things in, so let me know if you want me to break it up further 👍