[lldb/Plugins] Move SBTarget::GetExtendedCrashInformation to SBProcess

This patch moves the SB API method GetExtendedCrashInformation from
SBTarget to SBProcess since it only makes sense to call this method on a
sane process which might not be the case on a SBTarget object.

It also addresses some feedbacks received after landing the first patch
for the 'crash-info' feature.

Differential Revision: https://reviews.llvm.org/D75049



Signed-off-by: Med Ismail Bennani <medismail.bennani@gmail.com>