Support whitelist entries from class2greylist

Whitelist used to be the same as all entries in API stubs. This is no
longer true as libcore will generate hidden bridge methods which are
supposed to be whitelisted. CL in build/make calls class2greylist on
each boot classpath module to dump their list and this patch creates
a build rule for the new whitelist.

Bug: 112186571
Test: m appcompat, diff public-list.txt whitelist.txt
Change-Id: I7b3957ea9ed8bebb483609d94b1e6f169f4379dd