Improve Jolt implementation

[johannessen]

Jolt (“JSON Bolt”) in Neo4j 4.2 can replace our regex parsing of the old rest result format and should solve the issue of relevant metadata not being available in the server’s JSON response (e. g. neo4j/neo4j#12613).

This works via the HTTP Accept header, which is great for compatibility, but will entail some major changes to the driver.

[johannessen]

Jolt is available starting with driver version 0.21 by setting the jolt config option to a truthy value. Based on tests run so far, Jolt seems more reliable than JSON and is also significantly faster.

However, there is more work to be done:

• [ ] The Jolt implementation in 0.21 lacks result streaming: It always parses the entire Jolt response at once, before even returning from run().
  (In other words: $Neo4j::Driver::Result::Jolt::gather_results = 0 is unimplemented.)
• [ ] As of 0.21, Jolt event parsing has not been optimised.
• [x] Instead of having unit tests, the 0.21 Jolt result handler only contains lots of assertions.
• [x] Make sure Jolt works as expected before and after Neo4j 4.2.5.

[johannessen]

1fbca883375e98de5f06dbb4bea3aa135902609f, released as version 0.24, makes Jolt the default. Please be sure to report any issues.