fixed #10697 - split unmatchedSuppression from --enable=information

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First of all unmatchedSuppression has probably never worked properly. So depending on your configuration it might have been that have never seen such a warning at all or you had to deal with false positives. So you had to suppress these (probably globally) and that is a whole other thing (see below).

Secondly this is not very portable at all. Also depending on your configuration or just the underlying version of Cppcheck you will get these warnings. These might not apply to you so you want to get rid of them but they might show up for somebody else. So this is not something a regular user should not have enabled (this might also go for other messages in the category but one thing at a time). It is rather something you want to have within your CI. It seems like something that should go behind --check-config instead but since this requires the whole analysis to be run that is obviously not a fit.

Also suppressing these is an annoying chicken and egg problem (at least used to be). In case you have a version which no longer or not yet triggers any of the findings which needs to be suppressed you will get these warnings and then you have to suppress them. But if you do that and the suppression is actually used then you get a message that there was no unmatched suppression. This is probably something that should be avoided but something to look into after the unmatched suppression are actually reported as intended.

The reason the deprecation period is that short is because of the brokenness of this.