Enforce explicit use of project() command

The project() command documentation states:

The top-level CMakeLists.txt file for a project must contain a literal, direct call to the project() command; loading one through the include() command is not sufficient. If no such call exists CMake will implicitly add one to the top that enables the default languages (C and CXX).

Injecting the missing project() command is done before any call to cmake_minimum_required() and therefore its invocation to enable languages does not benefit from modern policy settings. This leads to problems like #17712 (closed).

We should consider ways to enforce explicit use of project(), such as a warning when the injection is done.

The canonical top-level CMakeLists.txt file should be:

cmake_minimum_required(VERSION 3.10) # or some other version
project(MyProject) # optionally list languages or use NONE to suppress them
# ... rest of the code