Extend fuzzing set up

[DavidKorczynski]

Adds a parse function in jv_parse.c that enables parsing using custom flags for the parser. This is then used by two fuzzers added as well.

This is to make sure fuzzing hits various code parts currently not fuzzed, e.g. stream_token:
https://storage.googleapis.com/oss-fuzz-coverage/jq/reports/20231125/linux/src/jq/src/jv_parse.c.html#L241

[DavidKorczynski]

Am not sure if adding jv_parse_custom_flags is too intrusive: if so, then I could wrap it in a macro that is only present for fuzzing builds?

[emanuele6]

I think it's ok to add a new function, but maybe make jv_parse_sized a wrapper that calls jv_parse_sized_custom_flags with 0 as flags to avoid duplication.

Thank you for adding more fuzzing!

PS: Could you also add a fuzzer for jv_dump functions (jv => JSON serialisation)?

[DavidKorczynski]

maybe make jv_parse_sized a wrapper that calls jv_parse_sized_custom_flags with 0 as flags to avoid duplication.

Done!

PS: Could you also add a fuzzer for jv_dump functions (jv => JSON serialisation)?

Added!

Once this is landed I'll add the new fuzzers to https://github.com/google/oss-fuzz/blob/master/projects/jq/build.sh

[emanuele6]

Thank you!