Add new "class2greylist" tool.

This extracts signatures of methods that have the @UsedByApps annotation
for generating the greylist. It will be integrated into the build to
replace many members on greylist.txt.

Test: $ atest class2greylisttest
Bug: 110868826
Change-Id: Ifaf5859b60076c051de6be5a912ef70734330ce7