Added ability to edit Animation in Frames instead of Seconds.

[Piet-G]

Added ability to edit Animation in Frames instead of Seconds. You can now choose which mode you want to edit in seconds/frames with a simple button:

You can also easily change at which framerate you want to edit the animation:

This does not alter any functionality to animations themselves and are contained wholy within the animation editor.

Currently there is still a need for a new icon for the newly introduced button (It will replace the all caps ENABLE_FRAME_MODE).

This is my first PR that's not just a bugfix, so some of the code might be a bit odd, any advice is appreciated!

This fixes #12165 and fixes #6149.

[fracteed]

Oh yeah, thanks for adding this! Many users have been begging for this for while now :) How does the snapping work now for frame mode? The last image has a snapping of 3, but there are 0,5,7,12,14 etc highlighted above. Should this be snapping to every third frame?

[Piet-G]

@fracteed Snapping can still be edited like you could in time mode, the last one just happens to have a snap of 3 because it converts whatever you snap choice was in time mode to frames in this case O.1 -> 3.

As for the highlighting,i have no idea what that is supposed to indicate, it doesn't seem to be the snap setting but I'm unsure what it does indicate. It seems rather odd indeed.

[fracteed]

@dualmatrix so if you are in frame mode and enter a snapping value of 2, you would be snapping to every second frame? I guess the "(s)' text would have to update itself to a "(f)" when switching modes.

[Piet-G]

@fracteed Yup that's how it works, and yeah that should probably be done, good catch.

[ghost]

Did a Win10 64-bit build and cherry picked this. I got this crash and stack trace when clicking on an AnimationPlayer from an existing project that had animation on it, or when making a new AnimationPlayer, the moment after creating a new animation and giving it a name.

[Piet-G]

@avencherus That doesn't look good, I'll go over the code and make sure that doesn't happen anymore. Thanks for testing 👍

[ghost]

No problem. Looked like an interesting feature and was curious. X)

[lupoDharkael]

I think this fixes #6149 too

[akien-mga]

Superseded by 4203266.