Ensure module load.php files really only load other code to prevent conflicts in standalone plugins

[felixarntz]

Summary

Fixes #667

Relevant technical choices

• Unless a module has already been using other files in a more specific way, this PR goes with the approach of splitting functions between a hooks.php file (functions that are used as hook callbacks) and a helper.php file (other functions, e.g. used by the hook functions).
• This PR looks like a massive change, but no code whatsoever was functionally modified. All functions touched were simply moved between files without modifications.
• The only code change that technically needs a closer review is all the load.php files, for whether they include the correct files and check for the correct function (any key function that is part of the respective module).

To avoid conflicts with other PRs, it would be great to review, iterate on, and merge this change ASAP.

Going forward, all modules will need to use their load.php file accordingly just to load other files. No actual code should be added directly to the load.php file of a module.

Checklist

• PR has either [Focus] or Infrastructure label.
• PR has a [Type] label.
• PR has a milestone or the no milestone label.

[felixarntz]

@mukeshpanchal27 Note that there will probably be merge conflicts between this PR and #670. We'll just have to fix them based on which PR gets merged first.

[mukeshpanchal27]

Thanks @felixarntz, The changes look good to me.