Arabic Stemmer improvement for Better Search Accuracy [LUCENE-8028]

HI, this is Ayah - bidi developer at IBM Egypt - Globalization Team, we are responsible to support Arabic at IBM products and services and as we use lucence at many of services, we found that it needs major improvement at Arabic stemmer, we implement the following two papers https://dl.acm.org/citation.cfm?id=1921657 and http://waset.org/publications/10005688/arabic-light-stemmer-for-better-search-accuracy to improve lucene arabic stemmer function and would like to open a Pull request to let you integrate it as a part of lucene

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Migrated from [LUCENE-8028](https://issues.apache.org/jira/browse/LUCENE-8028) by Ayah Shamandi, updated Dec 06 2017

Start by reviewing Lucene’s current Arabic stemmer function and the two linked papers. The issue does not name source files or tests; completion would require evaluating the proposed stemming implementation and providing a pull request that integrates it for improved Arabic search accuracy.

Written by the indexing model from the issue text.