Recently some include files got added to `common/include` which are
referenced by `core/include/keyman`. This change adds the necessary
code to install them in the same directory as the other include files.
Fixes#7490.
Adds infrastructure required to support caps lock control on keyboard
activation per #5822.
Keyboardprocessor implementation is currently a stub, and engines will
need corresponding updates to support the new API.
The name json.hpp conflicts with the JSON for Modern C++ library that
is also used by Developer. Renames json.hpp and json.cpp to jsonpp.hpp
and jsonpp.cpp aka "JSON Pretty Printer".