https://github.com/ruby/json/commit/1cdd2122d5

While it's not allowed by the spec, some parsers like Oj do
accept it, and it can be blocking a transition.

Having this feature can help people migrate.

https://github.com/ruby/json/commit/3459499cb3

It's the most likely control character so it's worth
giving a better error message for it.

https://github.com/ruby/json/commit/1da3fd9233

https://github.com/ruby/json/commit/e5e4fd558e

Fix: https://github.com/ruby/json/issues/912

In the case of surogate pairs we consume two backslashes, so
`json_next_backslash` need to ensure it's not sending us back in the
stream.

https://github.com/ruby/json/commit/0fce370c41

https://github.com/ruby/json/commit/4bdb2d14fe

https://github.com/ruby/json/commit/ccca602274

When serializing an Array, and one of the elements of the Array requires
calling `to_json`, if the depth is changed, it will be used for the next
entries, which wasn't the case before
https://github.com/ruby/json/commit/5abd43490714, and is not the case with
TruffleRuby and JRuby.

Additionally, with TruffleRuby and JRuby the state's depth after the
`to_json` call is used to close the Array, which isn't the case with
CRuby.

https://github.com/ruby/json/commit/386b36fde5

Otherwise it's very error prone.

https://github.com/ruby/json/commit/c54de70f90

`ALWAYS_INLINE()` and `NOINLINE()` are defined with one argument.

https://github.com/ruby/json/commit/8fb727901e