Try to report most mismatch errors on the 'impl' declaration. Only
report a mismatch error on the 'header' declaration if no error would be
otherwise reported on any 'impl' declaration in the compilation unit.
Also render declaration kind in the message
#KT-18447 In Progress
Use "-Xno-check-impl" to suppress checking whether the platform declaration
implementation has the "impl" modifier.
Do not check presence of fake overrides from platform class in the impl class,
otherwise there would be a lot of errors about the fact that
equals/hashCode/toString are not marked with the "impl" modifier
When matching platform and impl classifiers, ensure that each declaration from
the platform class scope is present in the impl class scope.
Note that the presence of the 'impl' modifier is not checked yet