92f1f8b31 Split off key_io_tests from base58_tests (Pieter Wuille)
119b0f85e Split key_io (address/key encodings) off from base58 (Pieter Wuille)
ebfe217b1 Stop using CBase58Data for ext keys (Pieter Wuille)
32e69fa0d Replace CBitcoinSecret with {Encode,Decode}Secret (Pieter Wuille)
Pull request description:
This PR contains some of the changes left as TODO in #11167 (and built on top of that PR). They are not intended for backporting.
This removes the `CBase58`, `CBitcoinSecret`, `CBitcoinExtKey`, and `CBitcoinExtPubKey` classes, in favor of simple `Encode`/`Decode` functions. Furthermore, all Bitcoin-specific logic (addresses, WIF, BIP32) is moved to `key_io.{h,cpp}`, leaving `base58.{h,cpp}` as a pure utility that implements the base58 encoding/decoding logic.
Tree-SHA512: a5962c0ed27ad53cbe00f22af432cf11aa530e3efc9798e25c004bc9ed1b5673db5df3956e398ee2c085e3a136ac8da69fe7a7d97a05fb2eb3be0b60d0479655