Make debugger tooltip API more general, have the engines check the
correct file type, figure out the expression and context from the text
editor.

Put common functionality in watchutils.cpp. In the CDB engine, check
whether a tooltip expression is a known variable within the stack frame
context. If so, retrieve via symbol group or dumpers. Cache by function
and expression.
Reviewed-by: hjk <qtc-committer@nokia.com>

Try to find qobject_p.h, if it exists and use its structures
to determine the child offset.

Add dumper calls, parser etc. Catch crashes
in the dumper functions.

Load in a 'well-defined' (temporary) breakpoint
at main().

Factor out watch function, improve debug output.

Details:  missing some more information, though..