compiler: detect suspicious JSONpath strings

[josephjclark]

Follow up to #781

JSON path strings in old adaptor versions to provide an attack vector to run arbritary code. I do not know if this allows breaking out of the sandbox.

https://security.snyk.io/vuln/SNYK-JS-JSONPATHPLUS-7945884

The compiler could detect suspicious json path strings and throw an error, refusing the execute the job.

If we detect a json path string like $.a.b.c with anything weird in it, like parenthesis, the compiler could throw.

Workflows which do use jsonpath strings should really only be using super simple expressions, and I'd be reasonably happy to throw if anything looks amiss in those strings. I think the pattern is fairly strong.