Auto-install cmake-format if the program is not found

[threeal]

This pull request introduces the capability to automatically install cmake-format using python -m pip if the program is not found on the system.

While it may be preferable to let users install their own cmake-format based on their preferences, this change proves useful in the context of GitHub Workflows. It simplifies the workflow by minimizing the need for explicit steps to install cmake-format, as the installation process is handled seamlessly by the script.

[TheLartians]

Hey, thanks for the PR! It definitely seems useful to have the format tools automatically installed. However, I see some issues with this approach as the configure script is now modifying the system's global state which is very unexpected.

A potential solution would be to install the cmake-format into a virtual environment, to not modify the global system, even though this can also be quite clunky.

[threeal]

@TheLartians I updated the code so the cmakelang will be installed on a virtual environment with version 0.6.13 specified.

[TheLartians]

Thanks for the changes, this looks quite good! Some thoughts:

• I think we still need to install pyyaml, otherwise it will fail if the config file is in yaml as the case in this repo.
• At this point, we could vent auto install both cmake-format and clang-format through the venv pip install clang-format==14.0.6 cmake_format==0.6.11 pyyaml.
• IMO it even makes sense to use the venv by default, even if clang/cmake-format is already installed on the system, as it prevents unexpected errors from version conflicts.
• We could consider allowing users to override the installed versions.
• To prevent unnecessary reinstallations of the venv, it might make sense to set the location of the virtual environment to the source directory of the Format.cmake project (and gitignore it). That way, it will be cached throughout different build directories when using a source cache with CPM.cmake.
• Finally, as this may have quite the impact on the initial configuration time, how about lazily initialising the venv only when the format targets are called so it is only installed when actually needed?

[threeal]

@TheLartians nice suggestion, i'll work on that later when i have times.