[Docs][C++][Parquet] Add API reference

[kou]

Describe the enhancement requested

We have Parquet API reference only for cpp/src/parquet/arrow for now. We should have Parquet API reference for cpp/src/parquet/ too.

See also: #49980

Component(s)

C++, Documentation, Parquet

[alexeyroytman]

Specifically, https://arrow.apache.org/docs/cpp/parquet.html#miscellaneous says:

Access to the Column Index, Offset Index and Bloom Filter structures is provided, but data read APIs do not currently make any use of them.

So, I'm looking for the external documentation on the PageIndexReader for using column/page index during file reading.