Switch hardened derivation marker to h in descriptors

This makes it easier to handle descriptor strings manually. E.g. an RPC call that takes an array of descriptors can now use '["desc": ".../0h/..."]'.

Both markers can still be parsed. The default for new descriptors is changed to h. In normalized form h is also used. For private keys the chosen marker is preserved in a round trip.

The hdkeypath field in getaddressinfo is also impacted by this change.

src/test/fuzz/parse_hd_keypath.cpp

@@ -18,6 +18,6 @@ FUZZ_TARGET(parse_hd_keypath)
 
     FuzzedDataProvider fuzzed_data_provider(buffer.data(), buffer.size());
     const std::vector<uint32_t> random_keypath = ConsumeRandomLengthIntegralVector<uint32_t>(fuzzed_data_provider);
-    (void)FormatHDKeypath(random_keypath);
+    (void)FormatHDKeypath(random_keypath, /*apostrophe=*/true); // WriteHDKeypath calls this with false
     (void)WriteHDKeypath(random_keypath);
 }