Added rfl::DefaultVal, resolves #534 #358

Job	Run time
windows-msvc-shared (AVRO)	8m 32s
windows-msvc-shared (FLEXBUFFERS)	6m 10s
windows-msvc-shared (CAPNPROTO)	8m 16s
windows-msvc-shared (MSGPACK)	4m 8s
windows-msvc-shared (CBOR)	8m 28s
windows-msvc-shared (JSON)	10m 29s
windows-msvc-shared (PARQUET)	39m 56s
windows-msvc-shared (UBJSON)	7m 22s
windows-msvc-shared (TOML)	3m 55s
windows-msvc-shared (YAML)	4m 6s
windows-msvc-shared (XML)	3m 41s
windows-msvc (CAPNPROTO)	1s
windows-msvc (MSGPACK)	3m 10s
windows-msvc (AVRO)	1s
windows-msvc (TOML)	1s
windows-msvc (XML)	2m 54s
windows-msvc (UBJSON)	5m 55s
windows-msvc (FLEXBUFFERS)	1s
windows-msvc (CBOR)	1s
windows-msvc (YAML)	1m 57s
windows-msvc (PARQUET)	5m 55s
windows-msvc (benchmarks)	1s
windows-msvc (JSON)	1s
	2h 5m 1s

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