Allow addtional file stem regex/subst for matching main include

[gabyx]

When following merge header placements (like qtbase), where B-p.h is a private header (-p) and B.cpp is its source file, than in B.cpp

#include "A.h"
#include "B-p.h" # is main include...

B-p.h cannot be detected to be the main include with the current settings.

Also we would like to have #53013
such that the include syntax does not matter above.

Not sure if the current logic could be made to include more possible file stems?

file = "B.bla.cpp" --> stem = "B.bla" , additionaStem = "B-p.bla"

where the additionalStem ist determined by a some regex/repl?

[llvmbot]

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