chore: Do not generate source files and use target_compile_definition… (#2369)

…s to set version

Advantages:
- not modifying src dir in build time (`git clean` will also remove
less)
- simpler codecov (if we decide to move it to separate stage in the
future)
- The cpp file is perfectly valid, so it will be treated as a C++ files
by all the tooling
- No need to use CMAKE_PROJECT_INCLUDE_BEFORE, should work fine without
it
- Instead of generating + recompiling, we will just be doing
recompilation of 1 file

.github/workflows/build_impl.yml

@@ -184,7 +184,6 @@ jobs:
 
       # This is run as part of the build job, because it requires the following:
       # - source code
-      # - generated source code (Build.cpp)
       # - conan packages
       # - .gcno files in build directory
       #