Summary:
This diff only moves the core of sonarkit to the xplat.
- This diff uses `fb_xplat_cxx_library` as a buck rule in xplat as it is the recommended way
- Updated few imports in the files which were not compiling with new buck function
- Due to the new way of import the OSS would break, so fixed it by changing the `podspec` file
Reviewed By: passy
Differential Revision: D8937414
fbshipit-source-id: 6e12cd049bedb496e7a6820be85b2535e70ba09b
