Tests to demonstrate the found issues

1. Constructor call parameters should be checked like methods
2. If local is assigned with a StringBuffer value, via a method call
that isn't a StringBuffer method, it cannot be changed

Change-Id: I4ccd1d662a078fb08c2b1144c1812d968e8c96f8
Signed-off-by: Lars Vogel <Lars.Vogel@vogella.com>
Signed-off-by: Jeff Johnston <jjohnstn@redhat.com>
Reviewed-on: https://git.eclipse.org/r/c/jdt/eclipse.jdt.ui/+/182335