[foreign] RFR 8213518: jextract should support --include-symbols option

[Sundararajan Athijegannathan]

jextract supports --exclude-symbols to filter out symbols from a header 
file. Sometimes we may want to include only specific symbols and exclude 
everything else. But it is bit difficult to write negative regexp 
filters with --exclude-symbols for such cases. It is better to have 
--include-symbols option as well.

Please review.

Bug: https://bugs.openjdk.java.net/browse/JDK-8213518
Webrev: https://cr.openjdk.java.net/~sundar/8213518/webrev.01/

Thanks,
-Sundar