Add SPI to get an array of all the installed plug-ins
https://bugs.webkit.org/show_bug.cgi?id=115688

Reviewed by Anders Carlsson.

* UIProcess/API/C/mac/WKContextPrivateMac.h:
* UIProcess/API/C/mac/WKContextPrivateMac.mm:
(createInfoDictionary):
Extract creation of info dictionary into helper.
(WKContextCopyPlugInInfoForBundleIdentifier):
Modified to use the new helper.
(WKContextGetInfoForInstalledPlugIns):
Added.


git-svn-id: http://svn.webkit.org/repository/webkit/trunk@149701 268f45cc-cd09-0410-ab3c-d52691b4dbfc