Update the Simple Coin Single-Signature Template to use Self-Spawn

[YaronWittenstein]

In Simple Coin Iteration #2 we add this Template implemented: #449

This time we need to add a new endpoint (SVM SDK #[endpoint]) that will receive as input:

• addr - The Address of the new Account to be created. (in a Pending state).
• value - The initial balance of that Account (to be transferred from the Target Account executing the code).

Notes

• We're supposed to compute ahead of time the Address of the Account since we know what the future Self-Spawn Transaction would look like (see Formula for computing an Account Address #247).

• For creating the Pending Account use the svm_account_create (see issue Implement host function: svm_account_create #466)