Goal

Make Variable to raise upon Subscription.
This implementation is meant to align SOAR's subscription behavior with R3's.

Description

R3's ReactiveProperty would publish its current value upon subscription.
Since ReactiveProperty have Value property, it aligns with SOAR's Variable.
For this reason, SOAR's Variable should have similar behavior.
On the other hand, R3's Subject doesn't have this behavior.
This aligns with SOAR's GameEvent.