- The LV2 bundle rather than the executable was incorrectly be signed

The new class hold a list of ChildProcesses and periodically checks
their return value until they report termination. On Linux this check
is necessary to avoid leaving zombie processes behind.

Even without this change the helpers would build correctly, but Xcode
would be unable to open them in the GUI and present them in red letters.

- Also refactored internals to use weak/shared pointers

- Refactored code to remove repetition and magic numbers

Co-authored-by: Tatsuya Shiozawa <shio.tatsu99@gmail.com>

To prevent too much disruption to people who have our public projects as
part of their build or testing systems we are temporarily ignoring a
warning about using Xcode 15.