Merge #20577: doc: libconsensus: add missing error code description, fix NBitcoin link

cb0b712 doc: libbitcoinconsensus: add missing error code description, fix NBitcoin link (Sebastian Falbesoner)

Pull request description:

  This PR improves the libbitcoinconsensus description in `shared-libraries.md` in two ways:
  * adds the missing error code description for `bitcoinconsensus_ERR_INVALID_FLAGS` (introduced by commit 5ca8ef2, PR #8976)
  * updates and fixes the link to the NBitcoin implementation (introduced by commit 3361edd, PR #6430)
      * the owner of the `NBitcoin` github repository changed from `NicolasDorier` to `MetacoSA` (redirection still worked though)
      * instead of dynamically referring to a file in master with a fixed line number (which is obviously always quickly outdated), use a permalink with a file numbers area

ACKs for top commit:
  MarcoFalke:
    cr ACK cb0b712
  harding:
    Code (documentation) review ACK cb0b712.  Text is clear and seems accurate, and the link checks out.

Tree-SHA512: 9840458db6fb40e71c9852104aefcec5abbaf5054c6123701181dd477cea8c81d3647f376b67692159adf577c9b6305b05b784728bf9f14a753fab5898075a4e

Author: fanquake

doc/shared-libraries.md

@@ -41,9 +41,10 @@ The interface is defined in the C header `bitcoinconsensus.h` located in `src/sc
 - `bitcoinconsensus_ERR_TX_SIZE_MISMATCH` - `txToLen` did not match with the size of `txTo`
 - `bitcoinconsensus_ERR_DESERIALIZE` - An error deserializing `txTo`
 - `bitcoinconsensus_ERR_AMOUNT_REQUIRED` - Input amount is required if WITNESS is used
+- `bitcoinconsensus_ERR_INVALID_FLAGS` - Script verification `flags` are invalid (i.e. not part of the libconsensus interface)
 
 ### Example Implementations
-- [NBitcoin](https://github.com/NicolasDorier/NBitcoin/blob/master/NBitcoin/Script.cs#L814) (.NET Bindings)
+- [NBitcoin](https://github.com/MetacoSA/NBitcoin/blob/5e1055cd7c4186dee4227c344af8892aea54faec/NBitcoin/Script.cs#L979-#L1031) (.NET Bindings)
 - [node-libbitcoinconsensus](https://github.com/bitpay/node-libbitcoinconsensus) (Node.js Bindings)
 - [java-libbitcoinconsensus](https://github.com/dexX7/java-libbitcoinconsensus) (Java Bindings)
 - [bitcoinconsensus-php](https://github.com/Bit-Wasp/bitcoinconsensus-php) (PHP Bindings)