[analyzer] Make CheckerManager::hasPathSensitiveCheckers() complete again

[analyzer] Make CheckerManager::hasPathSensitiveCheckers() complete again

It turns out that the CheckerManager::hasPathSensitiveCheckers() missed
checking for the BeginFunctionCheckers.
It seems like other callbacks are also missing:
 - ObjCMessageNilCheckers
 - BeginFunctionCheckers
 - NewAllocatorCheckers
 - PointerEscapeCheckers
 - EndOfTranslationUnitCheckers

In this patch, I wanted to use a fold-expression, but until C++17
arrives we are left with the old-school method.

When I tried to write a unittest I observed an interesting behavior. I
subscribed only to the BeginFunction event, it was not fired.
However, when I also defined the PreCall with an empty handler, suddenly
both fired.
I could add this test demonstrating the issue, but I don't think it
would serve much value in a long run. I don't expect regressions for
this.

However, I think it would be great to enforce the completeness of this
list in a runtime check.
I could not come up with a solution for this though.

PS: Thank you @Szelethus for helping me debugging this.

Differential Revision: https://reviews.llvm.org/D105101

Reviewed by: vsavchenko