[MERGE #2819 @obastemur]  xplat: add ChakraCoreHeaders target.
[MERGE #2819 @obastemur]  xplat: add ChakraCoreHeaders target.

Merge pull request #2819 from obastemur:headers

Rebased + updated @kphillisjr  's PR.

mrkmarron/ChakraCore,Microsoft/ChakraCore,mrkmarron/ChakraCore,Microsoft/ChakraCore,mrkmarron/ChakraCore,mrkmarron/ChakraCore,Microsoft/ChakraCore,mrkmarron/ChakraCore,mrkmarron/ChakraCore,Microsoft/ChakraCore,mrkmarron/ChakraCore,Microsoft/ChakraCore,Microsoft/ChakraCore