[LagFreeScreenshots] Add ScreenshotSavedEvent

[DragonPlayerX]

LagFreeScreenshots is replacing the whole saving process of images and the internal VRChat methods aren't called anymore than. So it would be helpful for other mods to have an event which is triggered after the screenshot file is saved and providing the file path.

My personal use would be for example the ScreenshotManager mod to realize automatic loading of new images without indexing the whole directories.

[knah]

Your PR was accepted, so closing this.