Use built-in Bazel JSON parser

With our maven_install.json it takes about 10-20 seconds to parse the JSON. Bazel just added a JSON parser so if this package switched to it, that bottleneck would go away.

https://github.com/bazelbuild/bazel/commit/6e47a409914d9f2ccb169482252f142c9fb503b8

Start with the current code path that parses maven_install.json, then read the linked Bazel commit to understand the built-in JSON parser. Compare the existing and replacement paths, and verify that parsing no longer accounts for the reported 10–20 second bottleneck.

Written by the indexing model from the issue text.