Parquet pages for different columns cannot be read in parallel

All ColumnChunkPageReader instances use the same decompressor. 

```java

BytesInputDecompressor decompressor = options.getCodecFactory().getDecompressor(descriptor.metadata.getCodec());
return new ColumnChunkPageReader(decompressor, pagesInChunk, dictionaryPage);
```
The CodecFactory caches the decompressors for every codec type returning the same instance on every getCompressor(codecName) call. See the caching happening here:

```java

@Override
public BytesDecompressor getDecompressor(CompressionCodecName codecName) {
BytesDecompressor decomp = decompressors.get(codecName);
if (decomp == null){
decomp = createDecompressor(codecName); decompressors.put(codecName, decomp);
}
return decomp;
}
 
```
 

If multiple threads try to read the pages belonging to different columns, they run into thread

safety issues. This issue prevents increasing the throughput at which applications can read parquet data by parallelizing page reads. 

**Reporter**: [Samarth Jain](https://issues.apache.org/jira/secure/ViewProfile.jspa?name=samarthjain) / @samarthjain
**Assignee**: [Samarth Jain](https://issues.apache.org/jira/secure/ViewProfile.jspa?name=samarthjain) / @samarthjain
#### PRs and other links:
- [GitHub Pull Request #668](https://github.com/apache/parquet-mr/pull/668)
- [GitHub Pull Request #670](https://github.com/apache/parquet-mr/pull/670)

_{**Note**: *This issue was originally created as [PARQUET-1641](https://issues.apache.org/jira/browse/PARQUET-1641). Please see the [migration documentation](https://issues.apache.org/jira/browse/PARQUET-2502) for further details.*}

Beginne mit ParquetFileReader.java ungefähr bei Zeile 1286 und CodecFactory.java ungefähr bei Zeile 197, um nachzuverfolgen, wie Dekompressoren von ColumnChunkPageReader-Instanzen gemeinsam genutzt werden. Sieh dir vor dem Beginn die Pull Requests #668 und #670 an und überprüfe anschließend, dass Seitenlesevorgänge für verschiedene Spalten parallel ausgeführt werden können, ohne dass das gemeldete Thread-Sicherheitsproblem auftritt.

Vom Indexierungsmodell aus dem Issue-Text verfasst.