feat: add initial People Playground mod development kit

extracted_wiki_content/internalReference/existifunderwater.txt

@@ -0,0 +1,16 @@
+URL: https://wiki.studiominus.nl/internalReference/ExistifUnderwater.html
+Title: People Playground Modding - ExistifUnderwater
+==================================================
+
+public class ExistifUnderwater
+Inherits MonoBehaviour
+Sets the GameObject's active state based on if the given point is under water
+Fields
+public Vector2 Offset
+The point that is checked
+
+public Space Space
+The space in which the point is checked
+
+public bool Invert
+Should the active state be inverted?