Ability to not play the frame of the 'toMarker' in 'AnimationView.play(fromMarker:toMarker:loopMode:completion:)'

[lennartstolz]

Hi! 👋

When working with markers it would be helpful to be able to specify whether the frame of the toMarker should be played or not.
This enables you to work with animation files providing mostly start markers - in case of a continuous animation, like the following:

Start prequel -> Start chorus -> Start FadeOut

If you, for example, would like to play the prequel once, loop the chorus x-times and then jump into the fade-out animation you'd need markers for Stop prequel and Stop chorus to make use of the .play(fromMarker:toMarker:loopMode:completion:) API¹. But all of those stop markers are basically just Start chorus - 1 frame and Start FadeOut - 1 frame.

The Android library does provide a boolean flag playEndMarkerStartFrame to handle this scenario:
(just a reference to one of its play methods)

https://github.com/airbnb/lottie-android/blob/108b1be70f115cda3c62d46d9f9808e6d465a3c0/lottie/src/main/java/com/airbnb/lottie/LottieDrawable.java#L761

Looking forward to get some input / thoughts about this. I am also happy to help with the implementation of a boolean flag (similar to Android) if you think it's a valuable addition to Lottie.

Best,
Lennart

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¹ Of course this is already possible with the current version, when calculating the frames yourself by using the frameTime(forMarker:) API and do the -1 manually but it would be handy to use the "better fitting" API.

[lennartstolz]

Implemented in #1772.