BHV-9859: Handle value validation in generic setter instead of change handler.

Issue
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The reset button in the Calendar sample no longer functions.

Fix
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It appears there has been a change in the order of evaluation of bindings and change handlers, which the Calendar sample is dependent upon (it attempts to transform the value during binding, assuming that the change handler has already run). We can instead pass the current date (via `new Date()`) instead of `null` as the value of `moon.Calendar` when resetting.

Enyo-DCO-1.1-Signed-off-by: Aaron Tam <aaron.tam@lge.com>