Add separate timeline snapping control to Animation Editor

[Arnklit]

This adds a separate toggle for timeline snapping (disabled by default as per @Calinou 's suggestion in the proposal)
Closes godotengine/godot-proposals#10225

godot.windows.editor.dev.x86_64_fFM33ZjKip.mp4

Both can still be toggled by holding Ctrl/Command

Note I changed the _get_editor_step() function to no longer check for whether snapping was enabled as it was already done before the function call in the _seek_value_changed function. Then I added a check the _animation_key_editor_seek function as well.

[TokageItLab]

It's feedback, but the icons and descriptions are unclear. Although I think it's fine for the function :)

With SnapTimeline and SnapKey, there is a misconception that it snaps to the grid of the timeline and the keys of other tracks (like smart grid); we need to avoid confusing it with such as the "grid snap" and "point snap" in Draw software / DCC software.

So more thought needs to be given to icons. It may be exaggerated to use Enum and explain it in text, but at least the description should be something like "Apply snapping to current time/key", not "Snap Timeline".

Thought:

[Arnklit]

@TokageItLab yeah good point. I'll improve the description. I quite like your icons idea... I'll fire up Inkscape and see what I can do!

[Arnklit]

Redesigned the icons and improved the descriptions and renamed a few things.

CquxyPfm4s.mp4

I'm not sure if that timeline snap icon reads well. it kind of looks like a taller version of the filter icon with a magnet next to it.

[TokageItLab]

The tooltip explanation needs some consideration, but I see that the icons and the behavior are fine.

[Arnklit]

@akien-mga rebased and conflict resolved

[Arnklit]

Sorry @TokageItLab , forgot to update that as I had to do a few and thought it was just the merge conflict on this one. Should be updated now as suggested.

[akien-mga]

Thanks!