[roll] Roll fuchsia [udp] Migrate to stable decode API

It turns out we can migrate to the stable API without breaking ABI. The
deserializer passes

  fidl::internal::WireFormatMetadataForVersion(fidl::internal::WireFormatVersion::kV2)

as the wire format metadata, because currently the serializer does not
write them.

Later, we can migrate to an evolvable ABI by soft-transitioning the
udp_serde protocol using the udp_serde version number, at which point we
can parse out the FIDL wire format metadata using:

  fidl::WireFormatMetadata::FromOpaque(opaque);

Where |opaque| is an uint64 obtained from the `wire_format_metadata()`
field of the encoding result object at sending time.

Performance: the new encoding API is a little bit slower. The new
decoding API is a little bit faster. Overall they sort of evens out:

RecvMsgMeta/Deserialize/IPv4/Empty               faster  0.847-0.878    111.7 +/- 1.7 ns    96.34 +/- 0.25 ns
RecvMsgMeta/Deserialize/IPv4/Full                faster  0.902-0.942    220.8 +/- 4.1 ns    203.43 +/- 0.58 ns
RecvMsgMeta/Deserialize/IPv6/Empty               faster  0.848-0.875    112.1 +/- 1.5 ns    96.57 +/- 0.28 ns
RecvMsgMeta/Deserialize/IPv6/Full                faster  0.932-0.944    232.29 +/- 0.98 ns  217.91 +/- 0.41 ns
RecvMsgMeta/Serialize/IPv4/Empty                 slower  1.017-1.026    357.41 +/- 0.37 ns  365.1 +/- 1.2 ns
RecvMsgMeta/Serialize/IPv4/Full                  slower  1.012-1.021    473.47 +/- 0.78 ns  481.3 +/- 1.4 ns
RecvMsgMeta/Serialize/IPv6/Empty                 slower  1.011-1.025    359.5 +/- 1.8 ns    365.98 +/- 0.55 ns
RecvMsgMeta/Serialize/IPv6/Full                  slower  1.014-1.026    492.6 +/- 1.3 ns    502.4 +/- 1.4 ns
RecvMsgMeta/SerializeThenDeserialize/IPv6/Empty  faster  0.991-0.999    455.02 +/- 0.52 ns  452.7 +/- 1.2 ns
RecvMsgMeta/SerializeThenDeserialize/IPv6/Full   faster  0.987-0.998    734.8 +/- 2.0 ns    729.2 +/- 1.9 ns
SendMsgMeta/Deserialize/IPv4/Empty               faster  0.863-0.872    85.10 +/- 0.38 ns   73.798 +/- 0.070 ns
SendMsgMeta/Deserialize/IPv4/Full                faster  0.917-0.931    188.8 +/- 1.3 ns    174.47 +/- 0.18 ns
SendMsgMeta/Deserialize/IPv6/Empty               faster  0.863-0.873    84.97 +/- 0.33 ns   73.76 +/- 0.15 ns
SendMsgMeta/Deserialize/IPv6/Full                faster  0.909-0.942    205.9 +/- 2.9 ns    190.50 +/- 0.72 ns
SendMsgMeta/Serialize/IPv4/Full                  slower  1.001-1.012    352.6 +/- 1.1 ns    354.92 +/- 0.71 ns
SendMsgMeta/Serialize/IPv6/Full                  slower  1.002-1.018    364.3 +/- 1.3 ns    367.9 +/- 1.6 ns
SendMsgMeta/SerializeThenDeserialize/IPv4/Empty  faster  0.960-0.970    333.48 +/- 0.41 ns  321.8 +/- 1.4 ns
SendMsgMeta/SerializeThenDeserialize/IPv4/Full   faster  0.973-0.982    535.72 +/- 0.67 ns  523.5 +/- 1.7 ns
SendMsgMeta/SerializeThenDeserialize/IPv6/Empty  faster  0.953-0.979    335.8 +/- 3.5 ns    324.3 +/- 1.1 ns
SendMsgMeta/SerializeThenDeserialize/IPv6/Full   faster  0.940-1.000    580 +/- 17 ns       561.8 +/- 1.2 ns

Original-Reviewed-on: https://fuchsia-review.googlesource.com/c/fuchsia/+/756833
Original-Revision: 5fdd067e87658d6738f004f6db1cd35d023f899b
GitOrigin-RevId: 7fa95b8b5df3506517c28dda18981406dd5db730
Change-Id: I6820d6afda9128f7f7aad825b81acd2e914633ac