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>

conanfile.py

@@ -151,9 +151,12 @@ class Xrpl(ConanFile):
             'libed25519.a',
             'libsecp256k1.a',
         ]
-        libxrpl.includedirs = ['include']
+        # TODO: Fix the protobufs to include each other relative to
+        # `include/`, not `include/ripple/proto/`.
+        libxrpl.includedirs = ['include', 'include/ripple/proto']
         libxrpl.requires = [
             'boost::boost',
             'openssl::crypto',
             'date::date',
+            'grpc::grpc++',
         ]