Currently the information severity messages are outputted as error
messages with Severity::Information. This causes constant confusion
as people think it as mildest error severity (and rightfully so).
When it was meant to be for printing messages about the checking
procedure itself (like missing header files etc).
So I'm adding a new function for the ErrorLogger for printing these
informative messages. This makes clear the distinction of errors
found from the code and messages related to the checking itself.
It also makes it easier for clients to handle these separately.
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