[analyzer] NFC: Change evalCall() to provide a CallEvent.

[analyzer] NFC: Change evalCall() to provide a CallEvent.

This changes the checker callback signature to use the modern, easy to
use interface. Additionally, this unblocks future work on allowing
checkers to implement evalCall() for calls that don't correspond to any
call-expression or require additional information that's only available
as part of the CallEvent, such as C++ constructors and destructors.

Differential Revision: https://reviews.llvm.org/D62440

git-svn-id: https://llvm.org/svn/llvm-project/cfe/trunk@363893 91177308-0d34-0410-b5e6-96231b3b80d8