Enhanced JsonInputFormatBenchmark.

[gianm]

Renames JsonLineReaderBenchmark to JsonInputFormatBenchmark, and enhances it to test various readers (JsonReader, JsonLineReader, JsonNodeReader) as well as to test with/without field discovery.

Results for parseAndRead:

Benchmark                              (discovery)  (readerTypeString)  Mode  Cnt     Score    Error  Units
JsonInputFormatBenchmark.parseAndRead        false              reader  avgt   10  3388.676 ± 45.400  ns/op
JsonInputFormatBenchmark.parseAndRead        false         node_reader  avgt   10  3442.947 ± 27.088  ns/op
JsonInputFormatBenchmark.parseAndRead        false         line_reader  avgt   10  2929.359 ± 52.594  ns/op
JsonInputFormatBenchmark.parseAndRead         true              reader  avgt   10  3622.374 ± 73.724  ns/op
JsonInputFormatBenchmark.parseAndRead         true         node_reader  avgt   10  3613.759 ± 26.548  ns/op
JsonInputFormatBenchmark.parseAndRead         true         line_reader  avgt   10  3009.840 ± 20.577  ns/op

[gianm]

This benchmark is also present in #15693.

[gianm]

No longer relevant since #15693 was merged.