Searcher Manger with support for Multi-Reader

[Shibi-bala]

Description

I'd like to use MultiReader inside my searcher manager, but currently there is only support for DirectoryReader. Not sure about the context for. why this was the case initially, seems specific to some desired use-case https://issues.apache.org/jira/browse/LUCENE-6087.

Anyway should be a 1-line change here:

lucene/lucene/core/src/java/org/apache/lucene/search/SearcherManager.java

Line 125 in 9e90fb5

public SearcherManager(DirectoryReader reader, SearcherFactory searcherFactory)

I found a relevant stack overflow question here:
https://stackoverflow.com/questions/49817453/searchermanager-and-multireader-in-lucene