Implement silent payments bip 352

[paulmillr]

Perhaps in a separate library?

https://github.com/bitcoin/bips/blob/master/bip-0352.mediawiki

https://github.com/louisinger/silentium

[deepsimulation]

I think support of this in this package is still cool & has overall alignment with what this package aims to enable. Separate package sounds cool too.

[mahnunchik]

+1 for separate library.

I think optional functions can be moved to a separate library, such as utxo selection, silent addressed etc. Leave the btc-signer only for signing Then, without the disadvantages of the main library, the number of utxo selection algorithms can be added

[jvgelder]

https://github.com/BlueWallet/SilentPayments/ implements it.
Maybe some of ecc and other related functionality can be moved to this library.

I was under the assumption a lot of people were still using bitcoinjs with tinysecp so I also started some work here: bitcoinjs/bitcoinjs-lib#2269