Merge bitcoin/bitcoin#16807: Let validateaddress locate error in Bech32 address

88cc481092 Modify copyright header on Bech32 code (Samuel Dobson)
5599813b80 Add lots of comments to Bech32 (Samuel Dobson)
2eb5792ec7 Add release notes for validateaddress Bech32 error detection (MeshCollider)
42d6a029e5 Refactor and add more tests for validateaddress (Samuel Dobson)
c4979f77c1 Add boost tests for bech32 error detection (MeshCollider)
02a7bdee42 Add error_locations to validateaddress RPC (Samuel Dobson)
b62b67e06c Add Bech32 error location function (Samuel Dobson)
0b06e720c0 More detailed error checking for base58 addresses (Samuel Dobson)

Pull request description:

  Addresses (partially) #16779 - no GUI change in this PR

  Adds a LocateError function the bech32 library, which is then called by `validateaddress` RPC, (and then eventually from a GUI tool too, future work). I think modifying validateaddress is nicer than adding a separate RPC for this.
  Includes tests.

  Based on https://github.com/sipa/bech32/blob/master/ecc/javascript/bech32_ecc.js
  Credit to sipa for that code

ACKs for top commit:
  laanwj:
    Code review and manually tested ACK 88cc481092
  ryanofsky:
    Code review ACK 88cc481092 with caveat that I only checked the new `LocateErrors` code to try to verify it didn't have unsafe or unexpected operations or loop forever or crash. Did not try to verify behavior corresponds to the spec. In the worst case bugs here should just affect error messages not actual decoding of addresses so this seemed ok.
  w0xlt:
    tACK 88cc481

Tree-SHA512: 9c7fe9745bc7527f80a30bd4c1e3034e16b96a02cc7f6c268f91bfad08a6965a8064fe44230aa3f87e4fa3c938f662ff4446bc682c83cb48c1a3f95cf4186688

doc/release-notes-16807.md

@@ -0,0 +1,6 @@
+Updated RPCs
+------------
+
+- The `validateaddress` RPC now optionally returns an `error_locations` array, with the indices of
+invalid characters in the address. For example, this will return the locations of up to two Bech32
+errors.