Update for view tags in next hf

[j-berman]

At the next hard fork, wallets will construct tx's where each output has a "view tag" stored on it. It's meant to speed up wallet scanning :) More on it here: monero-project/monero#8061

The smoothest way I could see how to add view tags to outputs in the core repo was by creating a new output type, which I called txout_to_tagged_key (after the fork, txout_to_key types won't be allowed anymore). This PR is necessary because of that change, unfortunately. To make the change as clean as I could, I added a helper function get_output_public_key to the core repo, so you can see in this PR the caller doesn't actually need to know the output type. I got rid of all txout_to_key types used in this repo and replaced with that helper function.

Hope you like! :)

[moneroexamples]

Thank you for your work on the tags and the PR to the explorer. Greatly appreciated.