Any reason?

All the analyzer classes should go into the same cpp file. And the header should just expose functions to construct the analyzer(like makeAnalyzer) or the high-level functions such as valueFlowForward.

This change requires duplicating the function declaration in both the header and cpp file and when adding an internal function the header needs to be updated, which doesnt make sense since this is not meant to be an interface, and adds more unnecessary work.

Makes sense.

I realized it myself even before your reply. The good thing is that I had the intermediate step of just moving all the involved code so the work could be mostly salvaged.

I considered moving more stuff into the added files but I wanted to start with something but did not think about this implementations basically just sitting behind interface (that's actually for I did for another in-progress refactoring so I should have realized). This stuff is just so tangled up that it takes several roundtrips until it get clear what could be extracted.