[C++] Replace RapidJSON in remaining JSON test utilities #51013

Describe the enhancement requested

The JSON test utilities use RapidJSON for JSON generation and pretty-printing, including test_common.h and JSON reader tests.

In addition, arrow/testing/gtest_util.cc still uses RapidJSON for parsing JSON data in TensorFromJSON().

Parent Issue: GH-35460.

Component(s)

C++