[analyzer] Add a new abstraction over all types of calls: CallEvent

[analyzer] Add a new abstraction over all types of calls: CallEvent

This is intended to replace CallOrObjCMessage, and is eventually intended to be
used for anything that cares more about /what/ is being called than /how/ it's
being called. For example, inlining destructors should be the same as inlining
blocks, and checking __attribute__((nonnull)) should apply to the allocator
calls generated by operator new.

git-svn-id: https://llvm.org/svn/llvm-project/cfe/trunk@159554 91177308-0d34-0410-b5e6-96231b3b80d8