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

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.

- Refactored code to remove repetition and magic numbers

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

This fixes a build failure on MacOS Sonoma when the copy plugin step
is enabled.

This fixes a warning when running xcodebuild directly

Enabling the hardened runtime also enables library validation, which
means that the manifest generator may not be able to load the built
plugin if the generator runs before the signing step.

The manifest generator tools should not be distributed/archived, so
disabling the hardened runtime for these targets is appropriate.