fix(json): don't crash on non-ASCII std::wstring / std::filesystem::p… #765

Job	Run time
windows-msvc-shared (YAML)	5m 15s
windows-msvc-shared (CAPNPROTO)	7m 50s
windows-msvc-shared (JSON)	11m 7s
windows-msvc-shared (FLEXBUFFERS)	6m 15s
windows-msvc-shared (MSGPACK)	4m 37s
windows-msvc-shared (TOML)	4m 37s
windows-msvc-shared (CBOR)	8m 52s
windows-msvc-shared (UBJSON)	8m 35s
windows-msvc-shared (XML)	4m 12s
windows-msvc-shared (AVRO)	7m 2s
windows-msvc-shared (BOOST_SERIALIZATION)	8m 19s
windows-msvc-shared (PARQUET)	39m 54s
windows-msvc (BOOST_SERIALIZATION)	7m 34s
windows-msvc (JSON)	12m 1s
windows-msvc (CEREAL)	4m 20s
windows-msvc (FLEXBUFFERS)	5m 29s
windows-msvc (CAPNPROTO)	8m 12s
windows-msvc (TOML)	3m 56s
windows-msvc (MSGPACK)	3m 48s
windows-msvc (CBOR)	8m 29s
windows-msvc (AVRO)	7m 22s
windows-msvc (benchmarks)	50m 57s
windows-msvc (YAML)	4m 23s
windows-msvc (UBJSON)	8m 17s
windows-msvc (XML)	4m 47s
windows-msvc (PARQUET)	36m 25s
	4h 42m 35s

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