Fix keyframe pasting to respect interpolation graph

[vezwork]

Demo

Before the fix:

1. the curve is slightly horizontally offset from the keyframes
2. the green y curve is copied from x, but does not match x's curve
3. the curve does not properly display default values when the keyframe has a type that does not match the track (not pictured)

after the fix:

1. the curve is correctly aligned with the keyframes
2. the green y is copied from x, and does match x
3. the curve correctly shows default values (not pictured)

Note

• also adds 'copy keyframe' to a single keyframe's context menu. Missed this on the first pass.

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[AriaMinaei]

The ! makes this function's type signature unreliable.