Add injectable locked coins function into the bank module.

[SpicyLemon]

Summary

Add a way to inject a "locked coins" function into the bank module as a way for other modules to indicate certain funds are locked.

Problem Definition

When we mark funds as being in escrow, it'd be nice if the bank module didn't still indicate that they are spendable.

Proposal

Similar to the SendRestrictionFn stuff, add a way to inject a LockedCoinsFn that returns an sdk.Coins indicating funds that are locked. Update the LockedCoins keeper function to call the injected function and add them to whatever it's currently returning.

---

For Admin Use

• Not duplicate issue
• Appropriate labels applied
• Appropriate contributors tagged
• Contributor assigned/self-assigned