Update json-c to 0.13.1

Summary:
Updated json-c to the latest version 0.13.1.

Changes:

• Bump the major version of the .so library generated up to 4.0 to avoid conflicts because some downstream packagers of json-c had already done their own bump to ".so.3" for a much older 0.12 release.
• Add const size_t json_c_object_sizeof()
• Avoid invalid free (and thus a segfault) when ref_count gets < 0
• Fix handling of custom double formats that include a ".0"
• Avoid uninitialized variable warnings in json_object_object_foreach
• Fix build for certain uClibc based systems.
• Add a top level fuzz directory for fuzzers run by OSS-Fuzz

Test Plan:
Installed and launched 'steam' which requires 'json-c-32bit' with everything working as expected.
Rebuilt and tested all the reverse dependencies of json-c successfully.

Reviewers: Triage Team, joebonrichie

Reviewed By: joebonrichie

Subscribers: joebonrichie, sunnyflunk

Differential Revision: https://dev.getsol.us/D4165