Wallet old coin selection can be improved

[Newly introduce indexes ](https://github.com/handshake-org/hsd/pull/928) for coins can be reused for the legacy coin selection types as well. This will reduce the number of items selected from the disk (will be useful for more advanced in memory coin selection algorithms, e.g. knapsack). Resolve coins from the WalletSource can also be reused for wallet in memory coin selection.

Start by reading the newly introduced coin indexes in pull request #928, then trace the legacy coin selection paths and WalletSource coin resolution mentioned here. Done means reusing those indexes and resolved coins to reduce disk-selected items while preserving existing wallet selection behavior.

Written by the indexing model from the issue text.