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.*}

从 ParquetFileReader.java 的第 1286 行附近和 CodecFactory.java 的第 197 行附近开始，跟踪解压缩器如何由 ColumnChunkPageReader 实例共享。在开始之前查看 pull requests #668 和 #670，然后验证不同列的页面读取可以并行运行，且不会出现报告的线程安全问题。

由索引模型根据 Issue 内容生成。