- split keyboard loading into loading KMX file into blob and then
loading the keyboard processor from the blob.
- deprecate `km_core_keyboard_load`
- move file access next to deprecated method. This is now the only place
that loads a file in Core; unit tests have some more places that
load files.
- introduce GTest and add unit tests for loading from blob
Part-of: #11293
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".
