[Refactor] PlannedPaymentsViewModel: using by delegation for mutable states

[shamim-emon]

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What's changed?

Describe with a few bullets what's new:

• I've updated PlannedPaymentsViewModel such that all it's mutableStates uses by delegate

Risk factors

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  In what cases won't your code work?
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Does this PR close any GitHub issues? (do not delete)

• Closes [Refactor] PlannedPaymentsViewModel: use by delegation for mutable states #3528

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