Malformed JSON in behaviour packs causes crash

Build: 423437

Summary:
Any JSON errors in behaviour packs cause an instant crash.

Impact: Minimal seeing as there shouldn't be malformed JSON in the first place, but I don't think it should necessarily cause an instant-crash. User should be informed of JSON errors.

Repro Steps: Load default behaviour pack and remove a comma or something from one of the entities json files. Load a world with behaviour pack on.

Observed Result: Instant crash and no warning

Expected Result: Previously in 1.1, malformed JSON would just nullify that entities behaviour file and still load the world. While an instant-crash makes malformed JSON easier to notice, a better way to go about it would be a header toast which displays JSON error notices or some other way to notify the user, yet still load the world successfully.

Screenshots: none, self-explanatory.