Fix the package recipe for consumers of libxrpl (#4631)

- "Rename" the type `LedgerInfo` to `LedgerHeader` (but leave an alias
  for `LedgerInfo` to not yet disturb existing uses). Put it in its own
  public header, named after itself, so that it is more easily found.
- Move the type `Fees` and NFT serialization functions into public
  (installed) headers.
- Compile the XRPL and gRPC protocol buffers directly into `libxrpl` and
  install their headers. Fix the Conan recipe to correctly export these
  types.

Addresses change (2) in
https://github.com/XRPLF/XRPL-Standards/discussions/121.

For context: This work supports Clio's dependence on libxrpl. Clio is
just an example consumer. These changes should benefit all current and
future consumers.

---------

Co-authored-by: cyan317 <120398799+cindyyan317@users.noreply.github.com>
Signed-off-by: Manoj Doshi <mdoshi@ripple.com>

src/test/overlay/compression_test.cpp

@@ -34,12 +34,12 @@
 #include <ripple/protocol/Sign.h>
 #include <ripple/protocol/digest.h>
 #include <ripple/protocol/jss.h>
+#include <ripple/protocol/messages.h>
 #include <ripple/shamap/SHAMapNodeID.h>
 #include <boost/asio/ip/address_v4.hpp>
 #include <boost/beast/core/multi_buffer.hpp>
 #include <boost/endian/conversion.hpp>
 #include <algorithm>
-#include <ripple.pb.h>
 #include <test/jtx/Account.h>
 #include <test/jtx/Env.h>
 #include <test/jtx/WSClient.h>