BHV-747: Do not animate slider when constrainToBgProgress is true and unclamped value is greater than bgProgress.

Issue
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When `constrainToBgProgress` is `true`, the slider animation can be seen animating outside the bounds of the current background progress.

Fix
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Only animate the slider if the current (and pre-clamped) slider value is less than the background progress value.

Enyo-DCO-1.1-Signed-off-by: Aaron Tam <aaron.tam@lge.com>