Private libraries (used by libmongoc) are not needed when building a client application with the shared library

They are only needed to build the library itself or when using the private library

Pkgconfig is mostly correct

• missing `Libs.private` may be considered as an issue
• missing `Requires: bson2`

mongocConfig.cmake requires some private libraries (libutf8proc, openssl, SASL2) which are not required

It also requires libbson, but this is correct (as some bson headers are included from the mongoc headers)

So building client using libmongoc and cmake fails when development packages for private libraries are not installed.