With this commit we enable the Jackson feature 'STRICT_DUPLICATE_DETECTION'
by default. This ensures that JSON keys are always unique. While this has
a performance impact, benchmarking has indicated that the typical drop in
indexing throughput is around 1 - 2%.
As a last resort, we allow users to still disable strict duplicate checks
by setting `-Des.json.strict_duplicate_detection=false` which is
intentionally undocumented.
Closes#19614