Testlib: Output function / total time along with crash dump.

Previously, only QXmlTestLogger had timers to take elapsed times
and log them. Move those into class QTestLog for access by
the loggers and output the times in the crash dump to make it
easier to spot hangs/recursion crashes.

Produces:

QFATAL : foo() Received signal 11
         Function time: 22ms Total time: 23ms

A crash occurred in ...
Function time: 24ms Total time: 26ms

Task-number: QTBUG-47370
Change-Id: Ia530a63104087daffc9a15f68c15d93378b9407e
Reviewed-by: Simon Hausmann <simon.hausmann@theqtcompany.com>