show some Cppcheck messages on file-level

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Workarounds for the messages in question will be outlined in an upcoming PR which fleshes out the Known Issues section in the documentation.

These should probably be shown as warnings but I chose to keep the severity provided by Cppcheck intact.

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This is a bit too much for 1.6.0 - we need to get the --xml stuff and the other fixes out first.

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I have a patch for Cppcheck ready to make missingInclude available with the normal analysis. I will add handling for it with a version check.

I will also hide all these additions in this PR behind the VERBOSE flag for now so it can be merged. I will make that flag available via the configuration later on.

[firewave]

I re-wrote the Known Issue section since it applies to some of these global warnings. I also enabled it in the regular build since these message might indicate reasons for false positive/negatives. The amount of messages will be reduced when we fix some of the known issues.

I will be dogfooding this for a few days before I move it out of the draft status.

Please also have a look at the documentation changes if they are understandable.

[firewave]

Seems to be working as expected. Need to go over the documentation changes one more time and then it should be good to go.

[firewave]

Cppcheck will now show all the individual missingInclude and missingIncludeSystem messages so I need to test this a bit more first. Probably will see if there are any more minor fixes I could put into 1.6.3.