[C++][Parquet] Allow partial prebuffer in parquet FileReader

[asfimport]

The current FileReader can only work in  one of the two modes, coalescing (when Prebuffer is called) and non-coalescing (when Prefufer is not called), due to the if statement here

Since Prebuffer is basically caching all specified column chunks, it would raise concerns on memory usage for systems with tight memory budget. In such scenarios, one may want to Prebuffer some small chunks while being able to read the rest chunks using  BufferedInputStream. 

Reporter: Jinpeng Zhou / @jp0317
Assignee: Jinpeng Zhou / @jp0317

PRs and other links:

• GitHub Pull Request #36192

_{Note: This issue was originally created as PARQUET-2316. Please see the migration documentation for further details.}

[asfimport]

Gang Wu / @wgtmac:
Issue resolved by pull request 36192
#36192