The logical breakpoints map was created as a side effect of
createUnrecoveredPanicBreakpoint or createFatalThrowBreakpoint, however
with an executable with incomplete debug info (that must be incomplete
in just the right way) both will fail and the logical breakpoint map
will never be created.
It's unknown how such an executable could be created, one easy way is
to debug a non-go executable.
Fixes#3114
Introduces a new TargetGroup abstraction that can be used to manage
multiple related targets.
No actual management of child processes is implemented here, this is
just a refactoring to make it possible to do that in the future.
Updates #2551