[sanitizer] move the coverage interface into a separate header, <sanitizer/coverage_interface.h>. NFC, except for the header name change. This may break existing users, but in this case it's better this way (not too many users so far)

llvm-svn: 228017
GitOrigin-RevId: cc0c773f76cdf978304e8e27e3de10db83dd951f
8 files changed