BHV-5887: Expose highlight/unhighlight functions for Spotlight muter.

Issue
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It appears that the `Spotlight Muter` was written before the `_bFocusOnScreen` was utilized heavily. This flag needs to be set to prevent multiple controls from being spotted when utilizing the `Muter`.

Fix
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The approach I took was to expose the `highlight` and `unhighlight` methods in `Spotlight`, in addition to adding a `bForce` parameter to force the highlight code to run regardless of mute state. The alternative would be to expose a method to set the `_bFocusOnScreen` flag and have mute/unmute make an extra function call.

Enyo-DCO-1.1-Signed-off-by: Aaron Tam <aaron.tam@lge.com>