SQlite3: better CMake FindSQlite3.cmake file

On macOS, with the standard FindSQlite3.cmake file, CMake finds the Framework system version of SQlite3, which is quite old. The script is this one:

https://github.com/Kitware/CMake/blob/master/Modules/FindSQLite3.cmake

Installing sqlite3 with Homebrew brings a newer version, but it is a keg-only formula, i.e. not linked by default. Also, using brew link --force sqlite3 gives a warning because it would shadow the system-wide version.

If we want to use a more recent version of SQlite3, we would better use an updated FindSQlite3.cmake file, like the one used in the valhalla project:

https://github.com/valhalla/valhalla/blob/master/cmake/FindSQLite3.cmake